Going first means you get higher-level Tranceunions out first. This is great for decks that focuses on pressure strategies, like Yukari (who focuses on increasing your attacks-per-turn anyway) and Overtrance Olga (rushing said card to immidiately rack advantages and make it harder for the opponent to fight back).

It works the other way as well- if you can get a really good defensive unit out early, you can leave the opponent run out of resources early in the game, specially if you can keep a column of gates alive, and have two units on each of those gates.