The boil doesn't have to be particularly vigorous, but the temp should be higher than just a simmer or steeping temp. I'm not certain there's a solid consensus, but there doesn't seem to be a compelling reason to boil the crap out of an all-grain and definitely not an extract. The reduction has taken place and you're essentially diluting the sugars enough to be able to add enough heat to get everything done.
Whether it's a full boil with bittering hops or a partial boil with 20 or 30 minute hop boil, most of the work you're doing is hop utilization. Gently rolling boil seems to be good and it's easier to control boil-off rate.There's some caramelization and some Maillard reaction (similar things, but different molecular processes...I don't understand the science there and I doubt seriously that even seasoned brewers really do, either) so that the character of the wort is cooked and transformed, hopefully in a good way, to get rid of the twang or green, unfinished quality.
I really want to do some full-boil extract because I can still taste a big difference in my all-grain brews and the partial boil/late addition ones. Those are quite fine and definitely way beyond the HME ones that I did, but they're not as smooth and lack malt character.