Synchro decks are notorious for being able to synchro summon again and again, meaning you could be drawing a whole bunch of cards from this guy over a few turns (or even in one turn, if youre lucky enough)
Not only can he Shift into play for a meager three ink, but he's worth two lore and gains a further two when he defeats someone in a challenge
Several Spell and Trap Cards can only be activated or gain additional effects when a certain monster is on the field, an example being the signature move series
Recently, Skilled Brown Magician, a card that allows you to search for proliferate, has become even more useful
2014-11-07 If a triggered ability granted by a lieutenant ability triggers, and in response to that trigger you lose control of your commander (causing the lieutenant to lose that ability), that triggered ability will still resolve.