it is recommended to activate this RA CAP UPDATE because it allows the network to know more about MS capabilities.
Regarding paging coordination specifically, it is not the MOST essential parameter. If it is not activated, then a MS which is only in a DL transfer (without any UL TBF ever established) will not be CS-pageable.
Since most MS will ALWAYS do at least 1 UL TBF (if only to TCP-ACK the DL TCP packets), this scenario will very rarely happen.
But as i said, RA CAP UPDATE cannot hurt…