If you've ever edited something with limited footage or too much footage you've probably gone back over it with a client and realized that you've used a shot more than once. Sometimes it's not obvious until you watch the edited piece, especially when you have limited footage and a precise script.
One trick I've used many times is to find the clip in question in the Bin and assign it a color label.
Highlight the clip
Hit Command + Option + any number key. I like using 6 for Green or 3 for Red.
You can toggle this while keeping an eye on the Timeline to see what gets labeled.
Sure there are other ways (like using Find) to locate what clips have been used but having a visual indicator of precisely where they are in the project helps me out tremendously since if they're far apart enough clients tend not to notice.