Actually, that's exactly the thing that SHOULD be forgotten. 5' long cheater bar is a great way to over-stress your equipment...start breaking chains and binders, ripping out stake pockets, not to mention potentially damaging the freight. Most winch bars these days have a funky looking end that fits over the handle of a snap binder, designed to "break" as binder snaps free...and those are "supposed" to only be used to release them, although I'd be lying if I said I never used mine to snug something up. Again, when using a cheater bar care must be used because you're putting a lot of tension on the chain. Pull it too close to it's breaking point just sitting there, there won't be enough left to hold the load while you're moving.
I use that type of winch bar to tighten my chains, it's a good three and a half foot bar, my rule of thumb is that if I can't tighten that with one hand on the bar I'm too tight. And I've said what you said about going too tight before and got attacked for it. My thinking is that if a chain is pulling down, using friction to secure the load, the chain should be tightened to close to the well. If it is being used to directly stop movement, it should have less pressure on it. Shouldn't be loose of course, just less tension on it. Of course none of us have pressure gauges telling us when it's tight enough. We have to just try to guess.
