[Danack]

The slowness appears to be caused by continual directory scanning. For me at least, turning off the "Refresh when files change" option, and so having to do "view, refresh" or Command-R, made SourceTree be zippy again.

And as I'm usually on a laptop, having less continued CPU usage is a good tradeoff against having to press refresh when I'm going to do something in SourceTree.

[Too]

Does not work, i've also heard from other sources that turning this option on makes it faster because then it uses some native file-changed-hooks instead of continuously polling the directory. For me both options are equally slow and many forum posts say the same. Sourcetree performance simply is crap and no fiddling with the options fixes this, nor should this fiddling be required. You can find bug tickets about performance issues dating back years but nothing happens, don't waste your time on sourcetree just because it looks shiny, use a tool that actually works.

[dcre]

Good point. I have auto-refresh off and it helps a lot, but I still find the UI feels laggy.