"Isn't it obvious?" Yamato asked, and he slowed his words slightly, as if he was speaking to a particularly idiotic child; "I am unfamiliar with this place and its dangers. What is safe for you, is not necessarily safe to me. Therefore, I would prefer to have something familiar, and known to be an ally, close at hand."

Cerberus could serve well as protection but... well, Yamato would just be comfortable with Alcor in close range.