When working with a large amount of items it's seldom a good idea to use a flat list... The ability to group those items is usually the way to go, and therefore the use of a tree is highly recommended.

That being said, it's exactly what could be improved in the Repository list of SourceTree. When working with a lot of repositories, SourceTree starts to become harder to use (and seems to me also slower). It would be so great to be able to create groups of repositories and close those groups when you don't need to access their content.

Refreshing also only displayed repositories would improve the responsiveness of the application and therefore the user experience.