In my opinion it makes a lot of sense. If you get the chance on how an OS is working, use it. It's great to know, how to build a kernel and do other stuff, most people seem not to know or not to care about. But I think this makes the difference between someone who is serious about pentesting and someone who is just looking to be spoonfed and always going the way of least resistance.
Seperates the Pentesters from the Kiddies