It really does depend on what you're developing and what you're shipping. Even minutia like language and build systems influence what's a convenient way to manage in progress work. I'm much more tolerant of dead-code/feature flag branches in certain parts of my codebase than others even. Sometimes you know exactly what you're building, but other times you're trying to sketch out an idea to see what it might look like and to get buy-in for a feature. You'll need to decide if you want to put the drag of partial work on everyone else who's making changes or on yourself to keep up with HEAD.

It's a choice.

All that said I think this feature in github is minor enough that it'll make what people were doing already more convenient (UX win) but won't substantially change how people work. It's just not dramatic enough.