in petrol engines yes egr can be good. as they mentioned it lowers throttling losses which increase fuel eficency. however diesels don't have throttle butterflys so that doesn't apply.
with diesels EGR simply means some loss in power. your reducing burning temps, fuel is not fully burnt so you lose out in economy and performance. then there is the nasty side effects of clogging manifolds and tempermental control systems. a big cause of cracked heads is often egr valve sticking open.
egr works ok on new motorrs but put on 100,000kms or more and its a different ball game.