Working in 120 format I almost start to salivate when I think about those big black and white negatives full of tonality that result in brilliant almost liquid looking prints. Also, the ability to shoot more than one type of film at a time using the same camera is real convenient. Big negatives make pictures on a contact sheet easier to see and big enlargements with minimal dust spotting. For me it would be almost the only film format I would ever want or need.
And then I get that phone call to photograph some really active kids. It's time to reach for the 35 because 36 shots without reloading are better than 12. And aside from some cameras used at horse races, there just aren't any 5 frame per second medium format cameras. And then there's the "I need prints right away" problem and it's a holiday weekend and the lab is closed on Monday, suddenly you're glad that 35 mm and c-41 one hour processing is nearly universal. Try taking a roll of 120 to your drugstore one-hour lab and see what kind of look you get.