I'm not overly familiar with the NHL version of this stuff, but with that said... I suspect the major benefit of doing this is that it gives access to those of us who cannot get it via our cable providers, etc. I don't know, so don't quite me on this, but I wonder if a subscription to it would also let you access streams on, say, a laptop computer for when you are not a home????? Again, I'm not sure.
Also... In baseball's version, I know the PS3 app let's you watch games from earlier in the day that you may have missed live. Wouldn't surprise me if NHL hockey does that, too, but I don't really know. If so, then I guess that's a potential benefit.
As for video quality... I tried the MLB basebell streams in the PS3 during a free preview weekend this summer. The quality of the streams over my wirelsss "g" network was very fuzzy and a little blocky, though watchable in a pinch (at least for baseball) but I wouldn't be satisfied with that quality for an entire season. That said... when I later hooked the modem up to the PS3 directly via Ethernet cable (for faster download speed) then the quality improved quite a bit. Still got the occassional blocks of a digital stream and maybe not always quite as smooth as a real TV broadcast, but things were pretty good. Maybe somewhere between DVD and HD quality??? Hard to say as I only got to watch the stuff briefly for one weekend. Definitely not perfection, though.