What does the corps help do and how is it useful?

For one thing, Corps gives you additional quests that you can take part into. You can earn items too for participating in Corps activities like boss battles where you may earn Officer fragments and token chests that usually contain speed-up items. Additionally, you get gathering buffs when gathering resources that are inside the premises of your Corps Command, or when gathering from your Corps Plastic Mold. Lastly, Corps offer you some kind of security blanket from rogue players plundering other player bases. Hope this helps!