Hey,
I just faced a scenario where i needed to launch a build config that i already have, only for a different branch.
A nice solution for this is to allow launching “custom” builds, and letting us select which branch will be used for that running build.
This feature exists in TeamCity from what i remember, and is very handy 
Right now, i had to duplicate the build config and change the branch it is using, which is kind of a hassle.