I use 8x10 and 4x5(same camera, reducing back for 4x5) because I like to. I also contact print(no room for an 8x10 enlarger), and frankly, an 8x10 print is big enough FOR ME. I've never been into monster prints, but I'll agree readily that there are times that call for a grand, super-size print to display the glory of what is on the negative.
and since most of my work is b/w now, I can develop/print everything myself(as I can with color neg as well), but shooting LF b&w affords me the ability to develop by inspection.
this can be done with roll films, but its much harder, due to the smaller negative.
and the advantage of shooting 8x10 IMO? Shoot an 8x10, and they you can trim the print to whatever size you want out of the scene

. cheaper/lighter than lugging around multiple sizes of film holders and reducing backs(or other cameras

).
I'm 21, but I feel this is my best way of working. Slower, more contemplative, and a very decisive approach. 35mm has its place in my work as well, along with 6x7cm, but the 6x7 I've found I like to contact print as well. Enlarging has always been somewhat of a pain for me, with calculations,etc... to do all the time to keep density the same. Seeing on the g/g EXACTLY what you will be printing affords one the ability to almost watch TV in front of you

.
and it brings up pretty girls too, asking what you're doing

. so of course I let them go under the darkcloth(with me to guide them of course

)
-Dan