I do think that after you release and more or less go "1.0" (even if you don't call it 1.0) you should start treating master as always-releasable. At that point if you have a lot of work to do and need checkpoints, do it on a branch. Same with major breaking change features. Keep master always ready so that you can release for bumping your upstream deps, releasing security fixes, or other interrupt driven housekeeping to stay current.