I know this is an older post but thought I would add to the pro's & cons.
I have a 2007 Yamaha Rhino 450 and absolutey love it. I have had a few atv's prior to the Rhino and my last machine was a Honda Foreman with 28" Mudlites, lift kit and a Dyno Jet kit.
The reason I went to a side by side was just having the ability for more cargo space. And since the Honda was straight axle, the wishbone suspension on all four corners was like night and day.
The machine is a good solid performer in the mud and 4x4 is excellent. Although it does not replace an atv in this category. Almost but not when it get's REALLY bad. I find the machine very noisey however and have snorkeled mine to get the engine sound a little quieter. Also the 450 is a tad under powered and if I were to do it again I would opt for the bigger cc's.
That being said I use my machine only for hunting and the 450 can pull a moose out no problem. Low gear with real 4x4 on all wheels is a tank.
The other thing with the box is it is great for deer hunters who are hauling out corn, apples and all your gear. I also have a double Kolpin gunboot on my back rack that I carry when moose hunting for example my rifle and a .410 for partridge. Or a rifle for your passenger of course.
Bear hunting and baiting is easy as you can throw your buckets etc. in the box and you are good to go.
Dragging in stands, setting them up, chainsaws hammers nails, I just grab a blue box and fill it with my portable saw and everything I need to go move or set up a new stand.
Just sooo much easier than trying to balance stuff on the racks of your bike.
I just recently put a lift on my UTV with new tires, jet kit, clutch sheave, and HID lights. Haven't taken it out yet but am looking forward to the upcoming seasons.
Drives like a Cadillac and won't spill your beer!
Here is an older pic before the add on's.