Re: To tension or not to tension, that is the question?
I used to say it is better to run one without. Now I would say the only thing better is running a chain tensioner that is spring loaded. The reason I say this is if your sprocket is a little off center then when you rotate your rear wheel the chain will have a tight spot and get loose then tight over and over. This will make the chain break faster and make it easier for the chain to jump off of the sprocket.
There is a franchise store called tractor supply that sells a spring tensioner. Check their website. The spring is sold seperately so make sure you get both. The tensioner is nice it has a rubber roller and ball bearings in it.
The springed tensioner keeps the chain tension the same all of the time even if your sprocket is off center a bit.