Why does Itunes have to update my software on my Iphone 5 all the time?

And it also takes up 3 hours to do so.

I need a specific and clear answer. Any apple product users?

Do you leave it and wait for it to Finnish or do you get bored and cancel it?
It shouldn't take that long everytime. I think What its doing is backing your iPhone up to your computer. If you look through the settings on iTunes you can set it so it doesn't back it up but then if your iPhone wipes everything of it for whatever reason then its not going to be backed up.
Hope this has helped a bit! X