The Utility effect in Ableton Live is great when you want to automate volume, but it only goes down to -35 dB which often can make complete fadeouts impossible. This is where the Dmixer comes in. It recreates the mixer section of a track and thus allows the gain to go down to -70 dB. It also contains the Mute button and a knob for panning.
This way for heaps more Max for Live devices & tips.