I tend to test a lot of software, sometimes for myself, other times because someone needs technical support, and I’ve not come across their type of troublesome application before. If it looks vaguely useful, I keep it (hence the need for roughly 900Gb of hard drive space on my PC, see my System Spec. post). If the program isn’t of use to me, I un-install it, and all is well…
At least that is the theory, however many programs do not properly un-install themselves fully, leaving behind various odds and ends; the worst location for these hang overs is the registry. Imagine everytime you had to do something in your life, you had to refer to a little pocket book for instructions. Now imagine you never cleared that book out. By the time you were mid-aged, you’d have information-overload in your book, and it would take far too long to look up instructions. Your PC suffers from the same sort of problems - the day you unpack it from the cardboard box, plug it in and start using it, it will be fairly nippy, do what you want it to (assuming you’ve installed the bare minimum of what you need), and not randomly slow down or even crash on you. As time goes by, more and more deitrus is left lying in your registry, and your PC will have issues carrying out the simplest tasks sometimes.
However, all is not lost, despite the actions of some of my friends, you DO NOT need to re-install Windows every 3 months! All you really need is a tool that can help to identify un-needed and incorrectly formed registry entries. If these problems are then removed or fixed, as appropriate, your PC can be spick and span again.
One such Registry Cleaning tool is jv16 PowerTools, which you can find out more about by clicking on the link.

The software can also tweak various aspects of your GUI, so you could find yourself in the enviable position of having a PC that performs even more quickly & stably than when it was brand new!