Agree with UK-Kev, slots are originally put there so that you can put a socket on an extension through it and turn then engine over, such as for a valve adjustment. The problem with the slots is that when you try to pull the socket and extension out, the slots are pretty stiff and it usually pulls your socket off the extension, dropping the socket to a random place you can’t reach. I’ll use a locking extension to prevent that from happening, but cutting the slots out seems like a well thought out upgrade. Whomever does your next valve adjustment will appreciate it.
Yep--there were originally slots there to access the crank pulley without having to remove the fender liner. I'd prefer having them intact, but I doubt anything bad would happen. It just looks bad, mainly.