I tend to think of alt-mouse as being used to pan... but it's more than that. What it really does is fix your POV on an object, so that you track it if it moves. (You can't directly alt-mouse into the sky--there's nothing there to fix your gaze on, SL thinks.) Every once in a while I happen to fix my gaze on someone rather than something, and then I am startled when that person heads out the door. :)
I think I've learned better, and what finally drove the lesson home was a contest I went to a while back, for best masked costume. (I had to go get a mask, and I thought I looked pretty good in it with the luna moth wings and pale green Empire dress. I didn't win--pout--but I did come out ahead after a couple of fortunate iterations of the low-stakes sploder.)
The contest took place at a club with dancing... and with dancers. They were kind of off to one corner, so I didn't notice them until someone mentioned them. I was curious, so... alt-mouse to the rescue. "Ah, there they are," I thought, and admired their lovely costumes...until I noticed the room slowly churning in the background, and my RL dinner gently called for my attention from its location in my RL stomach. They were dancing on a rotating dance floor, and from my position off that dance floor, I got to see the room move at a varying rate of speed.
Since then, I'm a bit more careful with alt-mouse...