First, there's the bit that he's an Ally! There are a lot of people out there who like to build Ally tribal decks, and Bruse Tarl can serve the function of Commander for those decks. Since he triggers Ally abilities, it's not a bad idea to explore this avenue when deck-building. But what's most fascinating is his repeatable ability. Whenever Bruse Tarl enters the battlefield or attacks, he gives a target creature you control double strike AND lifelink until end of turn. This could be himself, of course. As a 3/3 for 4 mana, he's not a bad candidate to be a Voltron-style Commander.
However, being a Partner Commander opens up possibilities. Since Bruse Tarl can gain the use of one or two other colors alongside a partner, the number of potential creatures with nasty combat damage triggering abilities that he can target increases dramatically. With double strike, not only are you gaining a lot of life, but you can create some pretty unfair advantages with combat-damage triggered abilities.