There are essentially three reasons why you should have registry repair software installed on your PC.
1. Increase performance
The most common complaint I hear as a systems administrator is that people complain how their PC performance has degraded since purchase. Each time you install or uninstall software or hardware on your PC the Windows registry gets changed. It gets bigger and gets fragmented. Windows needs to read the registry while booking your PC and also while you are running Windows. A big registry file which is fragmented takes longer to read/load than a brand new registry that is small and ordered.
Compare the registry with a wardrobe. If you store your clothes neatly in the wardrobe it will take you less time to find a particular piece of clothing. But if the clothes are not stacked neatly on the shelves and are not in the right place it would take a longer time to find it. Registry cleaners organise the registry so that Windows will find what it needs fast. These programs will also remove unused obsolete entries thus making the registry smaller.
2. Fixing PC Errors
If registry keys or parts of the registry are not stored in a correct way you get errors. Windows won't be able to find things and gives you cryptic error messages or "runtime errors". In older Windows versions you can even get the infamous "Blue Screens Of Death". Running a registry cleaner can fix these errors by fixing errors in the registry.
3. Save money
Some people reinstall their operating system twice a year to solve performance problems or errors they keep on getting. If you send your PC to a store or get a computer technician to look at it will cost you a bundle. Besides paying a bundle to get a complete reinstall or to get them to fix the errors you keep on getting, you won't be able to work behind the computer to get some work done. Buying registry repair software is a lot cheaper than getting your windows reinstalled or getting an computer engineer to look at the errors! Besides usually they will also use registry repair software to fix the errors for you.
Some people are afraid that this kind of software is hard to use or are afraid that they will break their PC using it. Fortunately most registry repair software will allow you to manually, or even better automatically, make a complete backup of your registry before youi make any changes to it. Make sure when you download your trial that the software has this option!
The usage of registry repair software is usually very easy and it will take a couple of minutes to scan your registry. After this scan it will show you the results and advise you to take action - for instance deletion of invalid keys. I would advise you to regulary scan your registry to fix possible errors and keep your PC running at peak performance!