This depends so much on what your work and industry is. I hear A/B and immediately think this is alien and inapplicable to me.

I work in game development and for the last six years I've spent most of my time specifically on optimization. A lot of that effort has been focused on cache behaviors. Not because it's fun, but because it's often the difference between being able to ship the game on weaker hardware (e.g. Nintendo Switch) or not.