A monopod can give you two or three or maybe four stops' worth of added camera stability, depending on how shaky you are to begin with. There are different types of monopods: I use mine ONLY with big, heavy telephotos that weight 7 pounds or more, plus an almost 4-lb camera, so I prefer a solid, aluminum two-section Bogen that's like 25 years old. For me, it's a great monopod, but I use it mostly standing upright, and occasionally, seated. So, I do not mind the two sections. But some people like the three- or four-section models which compact to a much higher degree, so they can be carried inside of a bag or backpack or whatnot.
But if you are shaky, I would say, yes, look into a monopod. I think it CAN help slow a fellow down, and it also helps "locate" the camera at a precise height, which can help, especially when shooting full-length, standing portraits, where you WANT TO LOWER THE CAMERA!!!!!!!!!!!! For the best "talls" on standing people, you must get the camera DOWN, well below chest height, and keep the back of the camera parallel with the standing people, and the monopod can really help with that, especially when using an eye-level camera.
Tall, full-length formal portraits are actually easier to shoot on a waist-level type camera, just for this reason.
Tripod-mounting is the way to do the formals, I think. It keeps the camera set up, and then you can pose people, and not need to constantly re-set the camera. It depends on how you've learned to shoot, but the majority of people who shoot wedding formal shots with the camera at eye-level turn in dumpy, stumpy looking brides and grooms. When you have a BIG group and the camera is on a tripod, you can look at the PEOPLE, and not need to squint through a finder, and you can see blinks and sideways glances much better that way.
I have to say however, there is ONE tripod model, just one, that makes using it a pleasure, and not a bunch of work, and I have owned one for close to two decades now:
http://www.google.com/search?q=Manf...oFpXmoASJuoDYDw&ved=0CEQQsAQ&biw=1657&bih=986
This is an "automatic" tripod, which can be raised, or lowered, and LOCKED with ONE FINGER squeeze of a trigger, and put into the EXACT, right height, in less than 2 seconds. The tripod is not just to steady the camera...it's more about respect, seriousness, keeping the "camera eye" still, and allowing you to be "a photographer" (free to move, cajole,tease,joke,laugh, clown around, whatever is needed) , and other stuff too.
THe above is THE tripod for professional people photographers. and it works unlike a slow, piece of crap, 4-section, 12-leg-lock carbon fiber or aluminum monstrosity. Those are BACKPACKING tripods...this is a professional-grtade tool, designed for FAST adjustment, up, down, and un-level ground, hillsides, kid-low, teenager middle, basketball player tall...this specific tripod is UN-equalled in terms of what is needed for people work. it is **NOT** like **ANY** other model ever made. There is ***NO*** comparing what this piece of equipment can do with the functioning of any other type of tripod. With 3- or 4-section legs and 9 or 12 or even six leg-locks to f*** around with for ever, single change of camera height, I would agree that a tripod is a pain in the butt. But this specific tripod is designed for professional portrait,event, and glamour work. It's heavy. But its sturdy and more-importantly, it's FAST to adjust.