The great thing about the masts we have on beachcats is that they are quite flexible. By trimming the mast (and hence the mainsail), you can change your mainsails profile to fit both lower and higher windspeeds. Most sailors sail in various conditions, depending on thermals, weathersystems, geography etc. So instead of having one sail for each windspeed/windrange (as larger monohulls often do), we make do by trimming the sails and mast. This system is quite successful!
In competitions, you are often only allowed to use one set of sails. If conditions change and you measured in with the "wrong" sail, you loose..

If you sail in places where you have very similar winds every day, tailoring a sail for those conditions are a very good idea (as you said).
For the 2000 olympics in Sidney, the gold medalists in the Tornado class showed up with a deep and draft forward jib. This jib allowed them to punch trough the waves on the racing area better than the others and they won the gold. (At least, that was the story I read)