I do not yet have a toyhauler of my own, but I've been shopping around for one after using my parent's non-toyhauler camper for several years. But my take on it is this...I'm sure it just depends on how you plan to use it.
For me, I have 3 kids, all girls. Just for privacy sake, it is nice for them to have their own room to go to when camping. They are younger so they go to bed a lot earlier than me and my wife. Plus, the separate garage is a good place to stash all the stuff that tends to clutter up the living quarters of the camper. However, if it were just me and my wife, a separate garage really wouldn't be necessary. But then again, we could get away with a lot smaller camper too. :)
Also, depending on what you want to haul, you can usually put a lot more toys in a toyhauler that does not have a separate garage. My buddy has a relatively small toyhauler. But he can easily stuff 3 full-size street bikes in it because he can pull one all the way up into the kitchen area. And when the toys are unloaded, the inside feels much bigger because it is all open.