I rarely need to open the software to make my car open the door automatically. Once in a blue moon I need to actually open the app to force it to connect. I actually can't remember the last time I needed to do that. It's normally completely seamless. The phone stays in my pocket - the doors unlock when I'm nearby, and lock when I leave.

That's my experience of course, other car apps might be much different. But that's an issue with the implementation, not the concept.