In Open splatfest battles, you get a synergy bonus to your Clout on winning if everybody on your team has some matching feature that gives you a team name, but you also get a nice personal bonus if you have exactly the same weapon, shoes, or hat as somebody else on your team. So between games in splatfests I'm always taking note of exactly what gear my teammates have so I can steal their look and get us some extra points for free. Is sabotaging myself by using unleveled gear and weapons I'm not used to worth the extra points? No, probably not, but it's fun! I also like to imagine that having the exact same gear as an ally looks intimidating, as if you're a coordinated team and talking on voice chat.
Also, probably a more generally useful point of advice: you can change hairstyle between games, and you'll get a bonus and a fancier team name if you all match! It's pretty rare that you'll end up in a team where you're the odd one out and can take advantage of this, but it's good to remember for when it happens.