Lots of things help swing the weight of a detector, and like ivanii said, swinging the big coils around would tire out Charles Atlas after a while. I've seen several different gizmos used, frequently some sort of bungee cord arrangement supporting part of the detector's weight from the detectorist's shoulders. The neatest thing I've seen, though, was one guy with a Sovereign and a huge coil (maybe an 18 incher) who had modified a FISHING POLE so the handle fit in a notch in the back of his belt, and he had something resembling football shoulder pads (but much lighter) to which the middle of the rod attached. A string ran from the top of the pole to just above the coil on his detector. The rod was flexible enough to allow easy movement and held the coil just above the surface. The pole supported 100% of the detector's weight, so the guy just moved his coil from side to side - and it would almost do it without any effort on his part. I tried to copy his setup with a rod blank I bought at the swap meet, but never felt comfortable with that rubbing against my shoulder (I didn't have his shoulder pads) and also found the detector was in my way when I tried to recover a target, and the thing wanted to go right in front of me even when I wanted it off to the side so I could recover the target. This thing does work, but only when there is nothing overhead (like on a beach or a athletic field) and I'm sure a good inventor could adapt the idea to make it really useful. Meanwhile, try the "swingy thing" bungee cord contraption sold by several detector stores that handle minelab.
