Integral. They help avoid spam and tailor your feed to make the experience better.

But at the same time, I think relays need to innovate and cater to certain areas/demographics/categories. Right now almost all the relays are just general discussion. I always envisioned relays with specific content like sports relays, bitcoin relays, etc. and then in clients you can filter which relays on your relay list you are writing/reading from at certain times or for certain notes.