Your computer's cooling systems usually contains of a fan. This fan pulls and throws air on the graphics card and the processor. But also attracts dust...

The dust usually builds a wall, resulting in the fan working without cooling. As months pass, the fan starts to make some noises, sign of its malfunction. The computer starts to work in high temperatures, you may feel the heat just by touching the outer cell (if it is laptop). The mainboard is going to fail, after some blue screen reboots...

So if you want to maintain the high quality of your laptop, you can give it to your technical lab for a cleaning service, changing at the same time the thermal conductive paste of the cards. Normally it costs about 20-30€, depending on the brand and difficulty :)