It might explain why Raphael used his vessel so hard, so the poor guy couldn't refuse consent. Of course that implies that consent is required each time. And if you remember Castiel did not jump at the chance to change from Claire back to Jimmy when logically Jimmy would be the more useful than Claire. A child would constantly be questioned & challenged where an adult would not be. Jimmy had to beg almost for Castiel to leave Claire for him. Castiel seemed to think that Jimmy had suffered enough and it would be better for Jimmy if he were freed. I think this is how it was meant to be between angels & their vessels. The angel is suppose to care for the well being of their vessel. When an angel does not it indicates the angel bears a resemblance to Lucifer, who does treat his vessels like they were condoms.
Angels are likely supposed to get permission so that they're not taking unwilling hosts and are supposed to limit the wear and tear on the bodies (unlike the demons who take whoever they want and, as they say many times on the show, 'ride their hosts hard').
However, a lot of angels have become courrpt and bend the rules by forcing a yes from potiential hosts and doing what they please with no regard to the people they're using.