There are a number of reasons that SourceTree may be performing poorly. Before you ask support or developers it would be helpful if you could go through the following list to help narrow down what the problem is, as well as a list of items to provide to support in the event of poor performance.

Things you can do to help SourceTree's performance

1. If you have a lot of untracked files, make sure the filters in SourceTree don't show these as Git/Hg take a long time to respond.
2. If you're using a system version of Git/Hg, make sure it's a recent version.
3. Make sure you have plenty of system resources available, CPU, RAM, plenty of hard disk space etc.
4. That you've got an up-to-date copy of SourceTree (we no longer publish to the App Store!)
5. That the repository location is local, i.e. on your hard disk rather than over a network or mounted volume.
6. Calling Git/Hg from the terminal performs as expected i.e. 'git log'
7. Make sure there's no applications constantly writing to disk at a repository location, this would cause SourceTree to constantly refresh.
8. Ensure files in your repository aren't locked (i.e. open in an editor) when trying to perform Git/Hg operations on them

Information to provide to support

1. Whether it's for Git/Hg and which version (embedded, system, and what system version if system)
2. System resources, CPU/RAM/HDD capacity (+ available hard disk space)
3. Where your repository is located, i.e. locally, on a mounted volume or over a network (SMB share etc.)
4. How many repositories you have in SourceTree 
5. How many repository windows you have open at one time
6. The version of SourceTree you're using
7. Operating system version.
8. The file filters you're using in SourceTree, i.e. 'Show Untracked'
9. If you have a lot of untracked files, please make a note of this also
10. Can you run 'git status' on that repository?
11. Log files located in:
    1. Windows: C:\Users\<username>\AppData\Local\Atlassian\SourceTree\sourcetree.log
    2. Mac: Open "Console" application and search for "SourceTree". Copy any relevant output.