A roo goes into a nestbox to help get it ready for the hen to lay, to show it is good enough and also safe.
A roo might also talk to his girls while they lay and sing the egg song with them when they are done.
Sometimes when my girls are upset about something in the coop, they will go and get the roo. He will come back and check the coop out, looking in nestboxes and talking to the girls. The girls will then get into the boxes and lay.
Makes me laugh to hear him singing with them. I think it's just natural for them to be protective of them.
Yes it is very natural. The roosters have a direct interest in the hens being able to lay a clutch of eggs, hatch chicks and raise them to add to his flock. Good roos will also help care for chicks - calling them to eat, stopping squabbles and even being a warm spot for babies to warm up.
Course - just because you might not have seen your roo do any of this, does not make him a "bad" roo -- he might just be shy