Computers are electronic devices and when they run they produce heat, often lots of heat.
The cooler the computers are when they are running the faster they will operate and more importantly they will not damage themselves. When the heat builds up in a computer it will begin damaging parts of the computer. Some computers are designed to shut off when they get too warm but most are not. Just like engines produce heat when running, computers do.
It is important that your desk top computers not be in small spaces that do not allow the air to circulate around them. It is important for that air flow to keep them cool. There are fans built in the desktop units to blow the heat out but if you do not have enough space around them the air goes nowhere and the computer gets hotter. Allow at least several inches all the way around and preferably about 6 or more inches of open space.
Laptops also produce heat and also have fans in them to force air out, but with the smallness of laptops and tablets there is not as much space ion the computer to allow air movement in them. In many cases the fans are blowing the air out of the bottom of the, For this reason it is not good to lay your laptop on your bed or sofa or carpet to use it and those surfaces will block the air and fan opening and ten the computer gets hot. Normally set then on a hard surface and they are built to set up a little Better is to get a cooling mat (a unit that sits under your laptop and has 1 or two fans in it and set your laptop on it and it will keep it cooler. If you are not sure if a laptop can get warm work on it with it sitting on your bare lets. They will get hot quick and in some cases can burn you.
Keep your computers with lots of air circulation and they will run better and longer and faster for you. If one of the fans in your computer (desktop, laptop or tablet) quits you need to replace it ASAP