Two reasons: nostalgia, being able to physically plug in a cartridge that you actually own and have the game save to it (which you can then play on a real Super Nintendo as well); also backup, actually being able to get a nice, completely legal copy of that cartridge that you own. Some people get a warm, fuzzy feeling to being 100% above board.
There's a third reason, too: Not all games have been dumped!
I own, for example, the PAL version of Bubble & Squeak for the Mega Drive. To my knowledge, this has not been dumped at all. As of when I last checked, back when I bought the cartridge (as I'm sure many of you know, I only emulate what I actually have), the only results I could find were dumping groups discussing how it had not been dumped. Now I can do so.
Should I ever be exceptionally lucky and encounter a situation where I end up possessing a game that was unreleased or is otherwise of some unique value (hey, it could happen...
), which I would absolutely not dare to trust anyone else with by sending it elsewhere, again, I can now deal with that situation, too.
I don't have the time to go through and re-dump everything I own, but for situations like that, or the occasions where I'm away with my Pandora but no internet access and come across a cache of games in a store, my Retrode 2 will be invaluable.
That, and supporting projects like this, was worth it, to me.