A touch of hiss and ambient noise can add to your guitar sound - especially if you prefer heavily distorted effects - but everyone needs a little peace and quiet now and again. Most guitar rigs suffer from noise and interference issues to some degree, and obviously, this is most noticeable in your stops, pauses and breaths.
A noise gate pedal will help reduce - or even eliminate - unwanted noise in those moments, helping to clean up your sound and sharpen the stops and starts in your riffs. Essentially, they act as a bottom limiter, letting you set the volume limit above which your signal can be heard. Anything quieter than this limit is muted. When you stop playing and your volume drops below the gate, it is muted. When you start playing again and your signal passes above the gate, it is unmuted. A noise gate is ideal for tightening up heavilly distorted tones allowing for cleaner, tighter playing.
Hiss, noise, buzz - a noise gate pedal will eradicate these pesky issues for you, and some pedals are so advanced that they even allow you to isolate and eliminate individual problem frequencies. Remember, as the classic philosophers said - “light can only be understood with the wisdom of darkness, just as loud, monstrously rocking distortion can only be understood by the itty-bitty-quiet-bits in-between”. So wise.