It requires far more HDD space than not using it because it doesn't seem to clean up after itself for a while. And if you get low on hard disk space your system grinds to a halt.
I dumped all of the non-important stuff (videos, music etc) into /Users/Shared and use Filevault only for dev and the size of it is fairly small. I haven't noticed any of the things you mentioned...
It requires far more HDD space than not using it because it doesn't seem to clean up after itself for a while. And if you get low on hard disk space your system grinds to a halt.