Although you can, because removable USB use solid-state memory which has a limited number of writes. They also use a swap mem bank and if you change a file on a USB stick, it isn't changed in situ - the block is actually copied out into the swap, modified and then copied back to another "free" location on the drive and the original block is zeroed out.
Now, if you have volume-based encryption, it will add data into every block on the USB (even the zeroed ones) so not only will every block have more writes to it than it needs for operation (all those encryption passes) but it will also slow the drive down because it will think that every block is filled and have to write more data in the swap. Although, newer USB sticks have a smarter caching system and you probably wouldn't see that much degradation.
SGN offers file-based encryption for USB sticks that mitigates all these problems. Since the drive is left in the clear and just the data being written is encrypted, you get to keep all the benefits of the USB drive and not reduce its lifetime.
