Plus ones for everyone?

What is yalls thoughts on plus ones? For everyone? Or maybe just friends I know who won't know anyone or if I know they are dating someone or are married? I've just had people recently tell me they are bringing people which I didn't expect them to (we did online rsvps) but I don't wanna be rude and tell them. I guess I feel like people don't understand the intimacy of weddings sometimes, or should at least ask if it's okay they bring someone before inviting that person, right?