Source Tree is a great git GUI on Mac OS.
But I found it may have memory leak issues.
When I run Source Tree one or two days, with two git and one hg repo window opened, it cosumes 2.7G memory of my 4G in total (shows in Activity Monitor, Real Mem), only left 20M free memory, makes system very very slow.
It always happened when I get back to the work in the morning of day, login window is very slow because Source Tree run out of all memory over the night, so I had to restart Source Tree once logged in.
It is really hard to test what causes it.