Connection limits also help relays create multiple plans that users can subscribe to. For instance, relays can offer a basic plan for kind 1 notes and a pro plan to store all drafts privately. 

Or a basic plan where clients can only make 1 request per second and a pro plan with 50 reqs per second.

They just need to let the Client know when different plans are active by sending the limits payload. 
https://github.com/nostr-protocol/nips/pull/1434