When using the float position with one of the top and tilt hydraulic cylinders, here are a few things that people will do.
With the top link they put it in float mode so that they can pull or push the ram to where it needs to be to hook up the link to the implement. Not a big deal, but there are people that feel it is much easier than having to go back and use the lever to get it extended just right.
With the side link when you are grading there are times-situations where to get the desired result about the only way to get that result is to use float mode. Again, not a HUGE deal, but very nice to have when you need it. Just makes the finished job that much better & easier to obtain.
Hope that explains it somewhat.