There are quite a number of reasons why it would be necessary to run a Windows registry scan, to see if there are errors or corrupt files within the registry.
For one, if your computer system is running slower than normal, and web sites are taking longer to load, then you should be looking into doing a Windows registry scan.
Also, if you are getting the dreaded blue screen that allows you to do absolutely nothing except unplug your computer from the wall and plug it back in; would be another reason to go for the scan.
What happens is, when you delete files from your computer, sometimes the registry doesn't fully and properly delete the file so it leaves an empty space in which your computer starts to search for every time you try to perform certain tasks.
This leaves unwanted entries in your registry and when they build up to a certain point, they start to negatively affect your computer, so the registry needs to be scanned, cleaned and repaired.
Just like any machine, your computer needs regular maintenance.
If you have experienced constant error messages for all different types of programs on your computer that are unrelated to each other like a chess game, and a calculator.
If you are getting error messages from anything you open, your registry is in need of a scan for sure.
Everybody should run a scan on their Windows registry now and then anyway, because you never know how close your computer is to starting to run slow and give you problems.
If you can prevent registry errors before they even occur that would be the best solution out of them all.
Basically, if any of these above symptoms/problems sound familiar to you...
you will most likely need to scan and repair your Windows registry.