Large complicated drawings on slower machines would be one reason to turn regenauto to off. Should there be a ton of lines with dashed type linetypes would be another. LTSCALE set to a low value, [deity of choice forbid] less then 1
Pan...wait.......do this..wait......
You can turn the prompt off somewhere, not sure where at the moment......Just looked it's the "EXPERT" system variable, it has many settings so you should look at them but setting it to 1 will disable the prompt "about to regen"