Maybe it's just me, but I find that they do make it a bit harder to get the rear wheel on, especially when fenders and larger tires are involved, because you have to slide the wheel forward and then sort of jockey it around to get it into the dropouts, at which point the tire can wedge up against the chainstay bridge, requiring you to sort of force it in (the fender and its mounting bolt reduce the amount of clearance here, and just generally get in the way). At least that's what happens on my Cross-Check but it no doubt depends on the frame geometry, tires, and other factors. It's not that big of a deal (how often do you take the rear wheel off anyway), but whenever I perform the same task on my vertical-dropout road bike, it always seems noticeably easier and less fussy.