Largely cultural in that it sends a huge message, but it does provide some measure of protection. It'll keep scratch damage a non-issue, and to an extent lessen larger injuries. It's not a game-changer, though, not by any stretch.
The copies wouldn't be able to do that, no; they're dividing up a single ki pool, not creating a bunch of new, smaller ones. Masques too are actually a transformation and a power limiter rather than a whole new body, so they would still split the ki. Great Apes, on the other hand, do draw from a separate source, so if you split off a single copy who then went Oozaru, both you and the copy would be at full strength. You cannot be fitted with multiple Masques.
Eh? Prophets?
You're pretty sure that that's Earth, huh?
By prophets I mean the Z Fighters, though Piccolo's... odd maze of a pedigree folds in an awful lot of people who wouldn't conventionally be considered.
I think a question needs to be asked first: What kind of message does it send?
Presumably, "I am here to punch things."