Article 27 of the General Data Protection Regulation requires that you appoint a representative in the EU as your point of contact for clients, customers and authorities regarding privacy matters. If you're based in the USA, and you're trading with or holding data on EU citizens, you must organize this to be GDPR compliant.
If you're a small mom and pop convenience store or a boutique coffee shop tucked away in a small village and your clientele are all locals, this doesn't apply to you.
But if you have clients and customers in the EU, if you want a global presence, and if you want to comply with the law, then this is not optional. Ya gotta have it.