The last ime a saw modifications like those was in sw. florida. Bugs particularly mud wasps would make a home anywhere they could get in so screen was commonly used to block off points of ingres.
If you live in a particularly Buggy area it may be a considera.
The opening on top seals around the filter so all air going in is filtered from that direction. The small nipple drain at the front would be un filtered air if not for the small filter there. The rest nipple goes into the PCV so also sealed from the outside air.
On both of mine the pcv hooks up to the enclosed plenum at the rear of the airbox and gets drawn into the velocity stacks via a plastic t on both sides.(plenum and t's are missing in pic.) The drain nipple goes in the front hole with nothing hooked up on the underside of the airbox, although it looks like a small drain hose should go there. The little round filter is more like a bushing for the filter to airbox. On the kn both the intake air and the drain hole are both in the same inner part of the filter where the unfiltered air is. at least thats how they were in the bikes before i took them off.