I don't wet print any medium format at the moment as for reasons of space I only have a little suitcase 35mm enlarger. However, when I did print both, the difference was apparent to me at pretty much all print sizes. Even when I scan 35mm and 120 negatives for web use I find I much prefer the shots from 120 [6x6 and 6x4.5 in my case].
It's about the tonality, and also the different look, including the transitions between in and out of focus that a longer lens combined with a larger format seems to bring. I've shot a little 5x4 and the step up between MF and 5x4 was (as per the obvious of the difference mentioned in the previous post) not enough for me to justify using 5x4 over 120.
I consider it a hallmark of the very best 35mm kit that I've used/owned that it approaches (but doesn't really completely match) something like the look I get from MF cameras. There are other reasons to shoot 35mm, and I use both formats, but the difference between 35mm and 120 is dramatic (for me, anyway).