Additional info / observed behavior:
While trying out Sourcetree and Sourcetree Enterprise out with a coworker of mine we observed a rather strange behavior: After installation I was able to choose between my coworkers account and mine. This allowed me to commit and push in his name.. Definitely not as intended.
To completely uninstall Sourcetree (regular version) one has to additionally delete files under USER/AppData/Local as well as USER/AppData/Roaming. We are not sure if additional steps have to be made for the Sourctree Enterprise version as well (to reinstate user to be unknown/reinstall from clean slate).