MySQL 8 has done some great improvements in the replication part. The purpose of MySQL 8 is all about scalability, performance, and security with utmost integrity of data, which is expected to be a game-changer in big data too.
Group replication basically takes care of committing transactions once most of the members in group replication have acknowledged the transaction received concurrently. This helps in a better throughput if the overall number of writes is not exceeding the capacity of the members in group replication. If there is a case where capacity is not planned appropriately, you would notice lags on affected members as compared to other members in the group.