You normally use the rubber feet for solid floors and the spikes for carpets. Yes, they make a big difference on the sound. On carpets, you can feel that the speakers are anchored to the floor and not "floating" on the carpet. While on solid floors (wood perhaps) there will be no vibration created by the speaker contact with the floor. You can experiment which set up you like better. Most probably you will like the traditional spikes on carpet and rubber on solid floors.