https://www.sonicwall.com/en-us/support/knowledge-base/170502920993204
This is news to me. I've often setup the IP pool to be on the LAN zone on small sites with only the built-in 1 or 2 licenses and haven't seen any problems myself, but sometimes users have complained about disconnections and performance issues which I've mostly thought to be from mobile connections they are using.
Have you been using LAN zone IP pools and encountered issues?