Many planes only have the bare minimum crew needed for gameplay, pilot and any machine gunners. Some of these planes had more crew such as spotters, radio operators, etc. For example the Japanese B5N had a crew of 3, pilot, navigator, and tail gunner.
Unlike ground vehicles you can’t really be switching around your plane crew when one of them gets shot because when you’re going down you’re going down, but it would be nice for immersion to have the full plane crew it’s supposed to be
Plus it gives you an extra soldier when you have to bail and fight on the ground!
So any plane that is missing any crew members should have them added. All planes should have the full crew they’re supposed to have