BuddyPress.org

A tag is for a specific release of BP: e.g. 1.2.1, 1.2.2, 1.2.3.
A branch is for a specific range of releases: e.g. 1.2.*

Any bug fixes will be applied into the 1.2 branch so it’s a good, mostly safe place, to stay if you want to run a version newer than 1.2.3 that isn’t going to add new functionality or mess up your site.