After using Sourcetree starts using CPU over 100% of it's capacity (e.g. 118.7%).
I am unable to tell exactly how to replicate this issue as it seems to happen intermittently and regardless of which Git repository I am working with in Sourcetree.
Generally it can happen after many hours that I leave a repository window opened in Sourcetree, or if I have do a Git merge between branches (even with just a few files/lines changed).
The only way to improve things is to close all Sourcetree windows and restart the app. The CPU usage will then stay at normal levels for some time (e.g. 0.5%).
I had this issue also with previous versions of Sourcetree.