LW for OSX uses a considerable amount. But more-so it is a VM (Virtual Memory) hog. The more shares, the more incompletes, the more searches, the more find sources you have the quicker it grows. ie: VM is where it stores temporary information on the HDD. All OSX programs use VM as does the system itself. Opening the Activity Monitor from the Utilities folder will show you how much VM each program has used. Of course, like RAM, as soon as you close the program, HDD space is returned.

The reason for the memory leaks is Java for OSX. It seems to have problems releasing memory when it has finished with it whilst the program is still open.

BTW I found I was having problems running LW in Ultrapeer mode. This was draining my system & sometimes knocking out my router. So you may wish to disable this option. You will find it in Prefs (keyboard shortcut: ⌘ ,) > Advanced > Performance & tick disable Ultrapeer capabilities.