ORIGINAL: MinnFlyer
Ah, the question of the century: How tight it "tight"?
There's no really good way to explain it accurately - fortunately, you have a good amount of leeway.
Yes!
It depends on the gauge of cable you are using too. I think the stuff they give you in ARTF's is quite light and has a fair bit of stretch. It will tolerate being tightened so that there's no slack in the system and you can pick it like a guitar string. Now, if you can do THAT, then it's a bit too tight, but there shouldn't be a hint of sagging or kinking in the wire.
I have a Flair models Pull-pull compensator in one of my models, but I can't seem to see them any more. Basically, this separates the pull-pull from the servo, and has a spring tensioned arm. If you overdo the tension, it gets taken up in the spring. The servo links to it with a rod.