I could see 3-1 Garchomp being played in Garchomp toolboxes, etc. decks, in which SP vs. SP matchup matters the most. After all, SP matchups are a lot about Garchomp C Lv.X sniping Garchomp Cs.
Though efficient use for 3-1 lineup would most probably require Premier Ball or a few. 3-1 extends the lineup most here, giving you the possibility to get the upper hand even if your opponent has got the Garchomp advantage due to faster start, etc.
Though 2-2 seems like the most usable lineup in tight lists.