In our view, there are very few places that could not be trimmed both easier and faster with a scythe - provided that one has an appropriate version of the scythe for the job, and of course, knows how to use it. Because we do have scythes customized for a great variety of tasks we use sickles only for the cutting of small plots of grain.

That said, sickles have been far more widespread around the world than scythes, and in many nations remain the primary tools for the harvesting of wild as well as cultivated plants. One reason is simply the cost difference; some of the globe's poorest peasants can still hardly afford a good sickle... Consequently, the introduction of scythes into many regions of Africa or Latin America (for duties where this tool would outperform either a machete or a sickle) has been much slower, or to date non-existent.

However, (regardless of the initial outlay difference) even a tool as inherently "sustainable" and efficient at the task for which it was designed as the scythe, may not be the tool of choice for regions where hands are many and cereals precious. Harvesting with a sickle (instead of a scythe) can, under some conditions (rain-beaten, tangled or overly ripe grain) significantly reduce kernel loss.

In the cultures where scythes and sickles were both common for a very long time (in Europe and the Near East) the sickles were/are used chiefly for two purposes:
a) cutting relatively small amounts of green forage for daily livestock feeding.
This is usually some distance away from the homestead where the animals are kept and the volume cut at a time is limited to what a person can carry back home - often on the back, though bicycles, wheelbarrows or two wheel carts are also used.
b) for harvesting of cereals - or at least some of the cereals. For instance, in Slovakia up until the early decades of 20th century, in regions where oats were long cut with a scythe, wheat and rye - both of which are not only more prone to grain head loss than oats, but also more precious as the ingredients of "our daily bread" -- were harvested more carefully, with sickles.

You see, we believe that a) the number of small/ family bread-sized grain plots may (or rather ought to!) become commonplace - possibly more so than North America has ever known. b) for many of these patches the sickle will be a more appropriate harvesting tool than the scythe.

We are well aware that the above two views do not reflect the presently popular notions, and furthermore, that the confirmed technocrats along with a hefty percentage of media-pacified general populace still believe the continued economic growth fairytale, and consequently would shake their heads with regard to "a". They simply consider such a change as "going backwards" - forgetting that every previously distinguished civilization has eventually moved "backwards", period.

Be it as it may, going by inquiries we receive on this subject, the majority of people planning to grow their own grain (for the family's table and perhaps a few chickens) seem to think that they have to obtain a "cradle scythe".
These well-intended folks have likely been influenced by The Scythe Book (or some of the Mother Earth-style articles) as well as the harvest paintings (Bruegel's the chief among them) - all of which, however unwittingly, romanticize the process and give little clue to the intricacies/challenges involved.

Well, for the benefit of the potential grain growers, here is some food for thought:

1.
It is definitely easier to learn how to use a sickle than a scythe.
Attaching a cradle to a "grass scythe" adds a dose of operational complexity, sometimes to the point of bringing beginners to tears.... To compound this fact, most of the snaths presently available via mail-order are (without some minor or major retrofitting) NOT best suited for grain harvesting (even if you are led to believe otherwise). Besides, the selection of cradles that can be purchased on distance (from anywhere on the globe) is very meager at best.

2.
The tall-standing grain fields and the perfectly uniform sheaves just cut from them that you see in the paintings exist, for the most part, in the paintings only.
In real life the rain and wind have always challenged the reaper. The rapidly changing weather patterns now suggest that the picture-perfect grain harvests may become even more rare -- and bread inevitably more precious.

We do by no means wish to discourage you from trying out the cradle. If tilling and sowing a sizable acreage is not a serious issue, and if it doesn't much matter that you loose a portion of your bread still in the field, harvesting with a scythe is certainly a worthwhile skill to practice.
There is plenty of indication, however, that the energy/means of field-scale tillage WILL be a serious issue in the future. Simultaneously, there is NO guarantee that surplus grain will be readily available for purchase should your own harvest fall short of expectations. Anyone paying attention to recent developments must already know that the probability of unexpected scenarios is, well, highly probable...

3.
The potential expediency of a scythe (if compared to a sickle) will only be realized on plots over a certain minimum size. It is somewhat difficult to accurately establish the "minimum", because there are too many variables with the condition of the crop being perhaps a major one. The next in line may be the number of available hands in relation to the volume to be cut coupled with how much each lost kernel matters. For instance, a family of four less-than-competent scythe users may be better off to cut their 1/3 acre of table wheat with sickles. But if they grow, say 2 acres or more of grains in total (some of it for livestock) learning to do the bulk of it with a scythe would, in the long run, save time cutting. (I put the cutting in italics, because it really is only relatively small portion of the time required from when you put the seed into the ground until the clean new kernels are ready to put into your mill.) Part of the "time loss" when using a sickle is made up while bundling the sheaves because the grain heads are better organized, and as a rule well-made sheaves are easier to stook so they shed rain if necessary.

There is a whole lot more that ought to be explained to the budding generation of would-be grain growers, but I am at a loss of what comprehensive source on the subject to recommend. If anyone reading this has discovered some serious attempt at "The Zen of Small Scale Grain Growing for the 21st Century" - please let us know so we can pass it on.