I was wondering how often this kind of optimizing is still done considering graphics power is as fast as it is and if this is a process you would only do for mobile games or games where you have hundreds of these objects on screen
That's a good question yyomimoto ,
I think @jlampel could give you a great answer.
I would suggest still optimize mesh objects the best you can, even with better graphics and faster CPU's. Remember that everyone has different hardware. Good practice when marketing a game would be to make it available to as many people as possible. If you only develop a game for high end hardware your losing thousands of potential sales.
Modern games will use higher resolution textures rather than denser meshes.
I hope this answers your question.
@adrian2301 hit the nail on the head here - optimization is done for pretty much every object of every game! The less computation that the mesh requires means more objects, more textures, or more lights in a scene, or if those things aren't needed, increased FPS. Powerful graphics cards enable us to do a lot of crazy things, but unfortunately forgetting mesh performance altogether is not one of them.