What does the code in the cd case of Skyrim PC version for? Do I really need it?

I just bought an original copy of skyrim and there is a code in the cd case, i have not yet installed the game. Do I still need the code even if i bought a cracked and pirated version of the game?What does the code in the cd case of Skyrim PC version for? Do I really need it?
The code is required in order to activate the game on Steam and actually play it. All copies of Skyrim require Steam on PC. Purchasing a pirated version of the game is illegal, not to mention a waste of money.What does the code in the cd case of Skyrim PC version for? Do I really need it?
The code on the case is what we in the PC gaming community call a CD-Key. Usually if you don't have a CD-Key you cannot even continue the install process or it will ask you for it before you can play the game. If you don't have one you can't play the game in most cases.