The Line6 M5 allows you to toggle between true bypass and DSP bypass. With the first, the pedal is removed from your signal chain when you're not using it. This can be great if you feel like your tone is being colored by the pedals in your chain. Also, if the pedal's power supply malfunctions, you will still hear your sound coming out of the amp, instead of cutting it out. With DSP bypass, the biggest advantage is that you will hear all the delay and reverb trails even after you switch off the effect, which gives it a much more natural feel than it does when it cuts out unexpectedly.