Why do Electric Guitars Need an Active Direct Box?

Guitars output a high impedance, unbalanced signal. Microphone inputs on mixers are low impedance and balanced. The direct box matches impedance while balancing the audio. Balanced audio allows you to run cable for long distances without unwanted noise. Guitars with passive pickups (the majority of electric guitars do not have active pickups) require an active direct box to properly preserve all the harmonics of the guitar's tone.