Well, like everything else ... it depends.
How old is your car? When's the last time you changed the coolant? Does your overflow bottle look like it has pretty and colorful kinda clear fluid, or is it more like a Progresso Beef Stew?
I flushed my 25 year old car when I got it. As long as I change the coolant regularly, and there are no head or intake gasket issues I may not need to do it again. BUT if I go to change the radiator again, just before I pull the old one I may do another flush. I use diluted CLR.
Most other flushes are either too caustic or too acidic. That means that while they're cleaning out your engine they're disintegrating gaskets, seals, sensors and thin plates. When you hear that someone had to change the waterpump because all that built up sludge was keeping it from leaking .. that ain't it.