The main benefit is thus: when you submit to iTunes through CD Baby, your album can't be browsed to via the genre browsing in that store. But with Tunecore, it can be. For a relatively well-known artist (e.g. Sister Machine Gun) that's not such a big deal, but for an unknown, it basically makes the difference between selling a record and not selling a record.
The other deciding factor is that it can take up to three months for a CD Baby digital submission to get in to iTunes, while Tunecore submissions take a week or two. It's basically impossible to get a CD Baby-submitted iTunes release to line up with its hard-copy counterpart, but that's not such a trick with Tunecore.
So, we're gonna give it a shot. I'll report back when we know if it makes a difference or not, but I'd be interested to hear if anyone else has Tunecore experiences they'd like to share.