The problem I’ve always had with learning assembly (arm in my case) was that I never really had a project to work on that would use any of that knowledge
There was a recent thread [1] optimizing some very primitive trig functions.
I recently watched a djb interview where he talked about the importance of fully utilizing available hardware [2 at 5:15]. That can be a good starting point, although at work its usually easier to just consume more resources than to use what you've got more efficiently.