Be it trad or sport, multi-pitch climbing is one of my favorite types of climbing. Like anything, if you do it enough, you develop your own approaches and preferences. One of my preferences is to carry two ATC-style belay devices, both capable of guide mode and at least one being an assisted brake device like the Mega Jul.
 
A light-load purist would probably laugh at my redundancy, but I have good reasons for doing this. (By the way, the Mega Jul is quite light!)

1. Having two devices saves time – Time efficiency is important for multi-pitch climbing, especially with longer climes. A 10 pitch climb with a 4-minute delay each pitch is 40 minutes – that could be the difference between being benighted or exiting with sun to spare. Having two ATCs saves time because when swinging pitches (where each person takes turn leading) you never have to take the new-leader off belay and the new-leader never even needs to tie into the anchor. Here is why/how:
   1. Leader 1 leads the first pitch, sets up the anchor, places the second on belay using the guide-mode on the non-brake-assisted device (if one device is not brake assisted).
   2. The second arrives at the belay station and is ready to lead pitch 2 (now referred to as the new-leader). Leave the new-leader in the guide-mode belay. Place the assisted brake ATC through your belay loop (the regular belay set-up) and place the new-leader on belay through the assisted brake ATC. The leader is always on belay and there is no need for the new-leader to tie into the anchor using a PAS.
   3. When the leader is ready to go, remove the rope from the guide-mode ATC. The new-leader is on belay and can climb right away.
2. Redundancy – If you (or your partner) accidentally drop a belay device you have a spare. Having both devices be ATCs capable of guide-mode, the climb can continue safely. You also have a device capable of rappelling (unlike if one of your devices is a GriGri).
   

 
Why have at least one of the ATCs be a brake-assisted device?

• For best safety, the device you use in “regular” belay mode (belaying from the harness belay loop not in guide mode) needs to be brake assisted on a multi-pitch. There are two reasons for this:
  1.  Multi-pitch climbs require more rope management. There are many times when you might need to take your brake hand off the rope to help feed/manage/untangle the rope.
  2. Multi-pitch climbs often carry more risk of rock fall. Should the belayer get knocked unconscious, the climber is protected (and in some scenarios the belayer is also better protected).