Laserfiche 9.1.1 SP2 can be considered the final update to the Laserfiche 9.1 line. It contains mostly fixes that are already in 9.2.0 and some fixes that were found since the release of 9.2.0. As for reasons to stay on 9.1.1 instead of upgrading to 9.2, I wouldn't say there are any major or compelling reasons to do so, but it ultimately depends on the customer's environment and if they can easily upgrade (while doing the due diligence in testing the process to ensure a smooth upgrade in production).