This could actually be useful for "open source but not open contribution" situations. It avoids the thing where people seeing that nice easy pull request button as somehow giving them the right to expect their contribution to be accepted.

"If you don't want contributors, why is it on [insert-forge-here] in the first place?" is a question I've seen asked in discussions about such things. Some people get personally insulted when their pull doesn't happen, even though the project states clearly ahead of time that this is how things are. Heck, some seem to be offended in advance that some hypothetical patch they might produce in future would be rejected.