When working on a local clone of Unreal Engine 4 repo (https://github.com/EpicGames/UnrealEngine - it's a private repo, but if you create an account at https://www.unrealengine.com/ you'll have free access to it), SourceTree often become unresponsive for several minutes (and sometimes crash too) making it unusable with that code base. I know that UE4 code base is "huge", but it's too bad to not be able to use SourceTree with it!