Reducing the number of relays you're using might not help you directly, but it makes it much easier for others to find your events and publish events that mention you to the right relays.

If you have a long list of relays, other users can't realistically connect to all of them. Clients usually need to fetch a lot of events and send many notifications for many users, not just you. So most clients only look at the first 2 to 4 relays you’ve configured, sometimes even fewer.

There are also many users who have way too many relays configured, and the first few relays in their list are actually broken or unreachable. This suggestion is mainly meant to remind those users.