Iris replication Improvement

Hi. I’m doing a research about Iris.
As I can see at this doc(Introduction To Iris In Unreal Engine | Unreal Engine 5.3 Documentation | Epic Developer Community), Iris got improvements by deleting anti-patterns that legacy replication system had).

Can I know which part was the anti-pattern from the previous replication system?
For example , as far as I know when using the previous system, if one client’s network got saturated, that unsent data was re-transmitted to every client again.

I want to know examples of the anti-patterns or any hints