Any blade's cutting is accomplished by using energy. The energy can be applied to the blade (example, a broadhead in flight) or to the object (example, pulling a rubber band over a stationary blade).
The energy is typically spread along the cutting edge of any blade. A serrated blade actually focuses energy to the points of the serrations, and that's why a very sharp serrated blade will often out-perform a smooth blade on tough jobs. It's the reason a serrated blade cuts a seatbelt, heavy rope, thick tendons and so on with less effort (energy) than a straight blade. I've used both blade types to butcher an entire bull moose...several in fact...and a very sharp serrated knife blade makes the job at least 33% easier. Of course all serrated blades aren't created equal, and there are different types of serrations which cut more effectively.
Yes, a serrated cut is a more jagged cut. Think of 20 little blades working at once instead of one continuous blade edge. A serrated blade actually has one disadvantage I've found, which is....on a knife at least....it tends to collect uncut hair inside the serrations, thus reducing cutting efficiency. I can't speak for a fast-flying serrated broadhead however.
I won't use a serrated broadhead for one reason: I only use resharpenable heads and I'm not about to sit down and sharpen all those little serrations. Period.