I agree with a good bit of what he says. Replacing a full exhaust isn't needed in most cases. Most people make changes for sound. Factories design the exhaust for the bike/engine setup.
What I don't agree with is the comment on not legal for street use. This a generalization and those comments should not be made. They are illegal in some or maybe most , not all locations.
I did change my exhaust can. I did not do it expecting performance gains. I did do it for weight reduction and to be perfectly honest, the stock can was butt ugly. I would be lying if I said I wasn't looking for a different sound. I wanted a more throaty sound but wasn't interested in going LOUD. If I want LOUD all I have to do is remove the baffle but I run with the baffle inserted.