The beret is not a good item for field wear, however there are times when it is the article of choice for many reasons: some good and some rediculous. Here are a couple of personal examples:
Because of what the beret symbolizes it becomes a pretty good psyop tool when you want to send a msg to someone that SF is alive and well in their back yard. We managed to get a Russian "trawler" siezed, bordered, and its cargo (which wasn't fish) removed by a host nation by passing the appropriate amount of information to the HN security folks in the port. To make sure that they (Russkies) understood who was behind it we casually strolled by the embarrassed crew and resident diplomatic mission that was on sight when all this was going down. It wasn't hard to spot the political officer who went ballistic and ran to get the ships captain.
Training missions that have high visibility where we want to make sure that US presence is noted is another area, but this is normally in a "garrison" environment. It also has been the article of choice when you are dealing with counterparts and they also are wearing their equivalent item when in uniform. In the field, it is definitely not the hear gear of choice-especially in a semi-permissive environment. Not only because it becomes a bullet magnet, but it is too damn hot, doesn't do anything to keep the sun out of your eyes, and as the leather band shrinks after it starts to dry out from all the sweat that has soaked it, it sort of brings your head to a point. This in itself is not a bad thing, because it allows you to easily sort out the real troopers from the others as those with pointy heads were the ones that were more concerned with profiling their head gear than with getting the job done
Now we always have had folks and units under which we have been placed in various command relationships that figure that unless you have spit shinned boots, haircuts, shaves, starched fatiques, and a beret on that you just are an undisciplined mob. These commanders under which we have fallen from time to time are of the "Weasely" Clark ilk that figure that if you look like a duck then you are therefore a duck dispite the fact that you can neither walk nor talk like a duck. The game plan here was normally to put the folks that looked like prize ducks in plain view while the real ganders did what they had come to do out of sight.