I use them for stability. However, I did need to remove them from one speaker stand because I needed the base to be lower, and that stand seems pretty stable without them. I'm getting new carpet and will probably initially try them out without stands, but I'm not concerned about putting them on the carpet.
Depending on your style of carpet, there may be no noticeable lasting effects from the spikes. At least, certainly no worse than the effects of any other piece of furniture that sits on the carpet for any period of time.