That's why they're called Temporary Files.
I also put brackets around the word 'temporary' because some programs just create files when you start them up for autosaves and stuff like that.
Then If I deleted it wouldnt it render other programs useless?
Browsers use save temporary files on the hard drive which are basically images of your most frequently visited web pages or any web page you visited since you started the computer up.
I'll use ComputerHope as an example. Every time you open up ComputerHope, you will notice that comes up almost instantly. This is because all the graphics are already saved on the computer, so they don't have to be called up and downloaded from the internet.
If you clear your temporary files (or Internet Cache) and try to load ComputerHope, it will come up slower and you can see the images being loaded.