Nowadays you can inspect someone's items from a full 30 yards away, but back in the day, you had to be within 10 yards in order to do it. And if someone moved out of that range while you were inspecting them, then the window showing all their items would go away.
I got fed up trying to catch up to people all the time when I wanted to inspect them, so as soon as I realized that an addon could help with this, I adopted it and never went back. SuperInspect has truly been the super hero addon of player inspection because not only does it preserve the inspecting window no matter how far away your target gets, it also gives you a good view of the target's graphical model, whether a player or an NPC. This feature lets you rotate or zoom in on the target model to your heart's content. Just love the look of that monster or enemy player in front of you but can't get close enough without getting attacked? Just use SuperInspect and zoom in!
There are several more features which make SuperInspect feel fleshed out and useful, such as colored borders for displayed items that indicate their quality, and total item bonuses added up from all your target's gear. It can also save the various characters you've looked at in each session so that you can look them up later. Mainly, though, SuperInspect just looks good, with a movable, scalable window, and even a pretty background behind each character that adds that certain flair that all good addons should have.