Steam Does not let you use your purchases Internet
There are many reasons not to use Steam but for the sake of brevity here are a few:
*If you buy a retail game that uses Steam you cannot play it unless you have internet access.
*Regardless if you buy the game at the shop Steam will still insist you download it over your internet connection to play it, even if this takes all day.
*You must have the Steam application on your computer to play your game and this sets itself to run on startup using your system resources until you manually disable it.
*The accounts system is seriously flawed and you can easily end up with multiple accounts you cannot access and randomly-generated passwords.
*If you accidentally register a game to one account Steam will not let you transfer it to your main account.
*Steam will not delete your personal information on request, even though this is illegal.
*Steam provides no email address, telephone number or mail address for customers to contact them (only a support ticket system), even though these are legal website requirements in Europe.
Be warned and do not make the mistake of purchasing Steam products!