The only difference in behaviour that I'm aware of is that if you make a 1:1 call then some features in a meeting are different, but as soon as the call has 3 people or if it's scheduled from an appointment it will be a meeting and have the normal capabilities.
I don't really understand why whiteboard is one of the things that gets limited, but it seems to be the case. If I press meet now in calendar I can start a whiteboard with just me in the meeting, I can also add one other person and it stays as a meeting.
The reason for the difference is a bit of a throwback to where the data goes. In a call it attempts to go direct from one device to another without a server being involved, which limits some functionality.