Sometimes a few greifers come to your sim and they use a trick to crash your sim or create lag. They do it by wearing a device which runs many scripts, and each script is created to do intense math calculations which take a lot of cpu time.
Wouldn't it be great if you had x-ray vision and could see who these people are? Now you can. Just wear my "person lag detector" and it will show you how many scripts a person has running, how much memory their scripts are using on your sim (some are designed to eat up all your sims memory), and how much time they are using of your cpu (some are designed to use up all your cpu with calculations). Get it free, now at Wizardry! :) All you do is attach the device to hud center or center2.