Once they decided to make GSR real they seemed to be split into the Grissom, Sara, Greg team and the Catherine, Nick, Warrick team on the majority of the cases.
Actually that happened after "Ch-Ch-Changes", well before GSR became a canon thing (and was delegated to wink-wink-nudge-nudge). After Nick was rescued from his kidnapping, Grissom told Ecklie he wanted his guys back, and they 're-joined' the teams.
The only split after that was when Sara went to Swing Shift to keep dating Grissom.
It may not have been an official split but if you watch starting around season 7 Sara very rarely worked with Nick, Warrick or Catherine. She was usually with Greg and Grissom except for any cases that were a full team effort. Compare seasons 7 & 8 to seasons 1-4 and you'll see that they didn't switch around the cast as much into different teams. It was like they were splitting them into 2 teams again without making it official like they did with Mea Culpa. Yes Nick had a great friendship with Warrick but I missed seeing him work with Grissom, or Sara, or Greg.
Susan