ISR out of Replica

Question

If the replica stays out of the ISR for very long time, then what does it tell us?

Answer 1

If the replica stays out of the ISR for very long time, or replica is not in synch with the ISR then it means that the follower server is not able to grasp data as fast the leader is doing. So basically the follower is not able to come up with the leader activities.

Hope this helps