Usualy it will be ok if you use the film with care. It dose affect the tempareture and heat dissipation of your laptop, but it's okay. After all the heat is mainly expeled from the hole on below or two sides. There are two little rubber buttons. They are screen holders, used to prevent the screen from completely sticking to the keyboard when you close the laptop. In this way, you needn't worry about the screen being crushed. Otherwise you can coat the screen with a film. Protective film dose have some advantages. It can prevent the words printed on the keys from disappearing and dust from getting into the computer host through keyboard.
It depends on what type of machine it is. If it is a high-quality one, it won't affect. But as for laptop, you may need a keyboard protective film. In fact, heat dissipation of laptop is not made by the keyboard but a specific opening. Therefore, we don't need to worry about the heat dissipation issue when we use the keyboard protective film.
It won't affect too much but it does affect because the heat is usually expelled from below or sides. It will be fine if the heat dissipation hole is not blocked. You can touch the underside of your laptop. There is an area which feels very hot because generally, it's where the CPU is set. The heat emmission of CPU is just made from below. And the above part is bare. If you cover the part with a layer of protective film, it will be like coat it with a thin quilt. Besides, metal emits heat really fast, and protective film can trap heat. Thus it dose affect the heat dissipation.
You'd better use a film. Even if the screen cracks, the film can make the computer looks like it's new~ ~ ~ laptop keyboard need to be protected well.
I suggest you'd better not use keyboard protective film because it will impede the heat dissipation of the computer. If you don't like your keyboard being dirty, you can use blush to clean it (usually included in laptop cleaning kit). And keeping it clean at other times.
