Originally Posted by AlanAZ
It would cause increased belt wear and pre-mature belt failure -- that could leave you stranded somewhere, and could, outside chance, damage the A/C compressor.
Check that the belt is running in a flat plane between all the pulleys, and the tensioner is not forward or back. Look for wear on the edge of the belt. A couple of people have reported broken mounting bolt on the tensioner, look for that. See the above thread for details and photos.
I had the same issue with a crooked tensioner and decided it was best to play it safe and change it out for all the reason quoted. It's a pretty simple job, even coming from someone with limited skills like myself. The last thing you want is that belt coming off while you are driving.