The relays Iris uses can change over time since they reflect the content you're viewing.
You can add, remove and disable (and enable with ☑) relays. By saving publicly the current relay list is published and you can use it on other clients.
Backup and Restore features include your relay list.
Settings / Network
Iris caches profiles, follows and the latest notes for a faster and better user experience.
Iris stores a few of the latest messages, contacts and metadata for a better user experience.
Iris asks for 1000 latest events from known users initially. Some relays don't like the large authors filter (100-2000). Then it subscribes to all upcoming messages but discards those that are from unknown authors. When you open someone's profile, all their events are queried.