Hi,
We're using central admin approved InfoPath 2010 forms extensively, and have made regular changes and deployment in our dev environments.
Overtime, central admin management pages became slower and slower, and occasionally, we'd see giant 2-GB log files (most of them saying delete FT-01-xxx folders).
I've noticed that Form Server seems to be keeping multiple copies of old form templates around, and tried these steps:
1. Retract my form from site collections.
2. Remove form from farm (heh! try saying that super quick 10 times)
3. Now I go and see my SharePointRoot\Template\Features folder and see that there are still many folders left behind.

4. Manually move (because I'm scared to delete them) them to another folder elsewhere so Form Server can't see this folder anymore.
5. Go back to central administration and re-upload / activate to site collection.
Results:
1. All my existing forms seems to continue to work.
2. The central admin pages are a LOT quicker.
3. No more giant log files.
But I'm not sure what they are used for, can they really be safely deleted?