Prolong the life of your carpet by having your carpets stretched. Stretching is more then just with a knee kicker. A power stretcher is required to stretch the carpet the whole length of the room  When you have ripples in the middle of your room, that's a sign of needing your carpets stretched, of course.  Another way is to go to the middle of your carpet, grab the carpet and lift, if you can pick it up three inches or so, that  is an earlier sign of needing your carpet stretched.