Too Much Tension might cause early failure.
I have only one cars worth of experience (87 300E) but in recently installing a new water pump I had to study this tensioner to see if it also needed replacement. What I decided is that if you re-use a tensioner you should not over tighten it or it may fail very quickly. The problem comes when you set the little pointer back at the loose end of the scale (just like the book instructs). This was good advice IF the tensioner was new, BUT if you are re-installing a used one I THINK you should only set the pointer to the distance it retracted to when you loosened it while removing it. Did you notice that it did not come back to the loose end of the scale? It had taken a "set" from use and heat. So if you start THERE and tighten it to the required end mark (tight) you should be approx. where it was running before. If you place the whole thing under too much tension you invite bearing failures on alt. and idler pulleys and tensioner unit, and the belt itself. ??? Am I thinking correctly? This is the way I set mine up and it seems to be doing great with a new belt and water pump.
Good luck to you,