The average person buys a new computer every 4 years. During that time, quite a bit can happen to slow down your machine. One of the most destructive though, is dust.
If your machine starts to clog and fill with dust, a few things will happen. In the beginning, it will just run slightly warmer than normal. But as the machine ages, more dust will accumulate, and it creates a downward spiral. Eventually, heatsinks on the cpu and/or graphics card become clogged with dust, which means less or even no air will be allowed to pass over the fins of the heatsink to cool it down.
Heat kills computers. The hotter your machine runs, the shorter its lifespan will be.
A good rule is to at least clean out your computer every 6 months. If you want to really stay on top of things though, a span of around 3 months might be better to target. That is a suggested time frame though. If your machine is on the floor, or in a dusty environment like a warehouse, then it may need to be done much more often.
Do yourself a favor and spend a few minutes to clean out your computer this spring!