It's a pain on the CPU though if you have a lot of non-transform/opacity changes though. It's much better to just animate the elements that you want animated and leave the rest alone.

I hadn't considered that, although it shouldn't create waste, right? Presumably, unchanging properties with transitions enabled don't add any work to be done. If it's only the ones that change, and if I really do want all of those to transition, there's no problem.

Right, but a lot of properties you probably don't want animated, and modern frameworks also reuse dom elements sometimes, so it might create a lot of lag and weird transitions between elements that you didn't foresee.