When editing an LLB under Mac OS X, the temporary copy of the LLB is not deleted. To see this, open an LLB, modify a file and save it back to the LLB. You will find that a file has been created:
/var/tmp/folders.NNN/TemporaryItems/tarc########.llb
Where NNN is your numerical user id and ######### is some sort of unique ID for the library. If you look at your Temporary items folder you may find a lot of old LLBs in there taking up space.
Look at the folder, by opening a Finder window, type Command-Shift-G and then enter /var/tmp. Then you can fidn the correct folders.NNN sub folder. This folder is NOT cleared on reboot so it can get a lot of stuff in it.
/var/tmp/folders.NNN/TemporaryItems/