Most forms of Isolation aim to reduce the amount of external (and internal) vibration affects your system, whether thats your speakers, turntable, amplifier etc. These vibrations may not seem noticeable to you, however, Hi-Fi equipment can be extremely sensitive and even micro-vibrations can introduce noise to your music. Two great examples are for Speakers and Turntables. If a speaker receives excess vibrations from an external source, this can affect the movement of the drivers and directly affect what you can hear. Similarly with Turntables, any excess vibrations can affect the movement of the cartridge which ultimately means a change in the musical information. All of these situations mean you won't be able to hear your system and your music as it was intended. Even some simple isolation for your most sensitive equipment can go a long way to improving your listening sessions, and the more isolation you introduce, the lower your overall noise floor can be.