No it will not effect. Steam is well known and in some cases loved... its the best download platform atm followed by D2D (direct to drive). the 1 you want to be warey of is origin.. it is basicaly spyware and is classed as malware by quite a few antivirus and antimalware suites.

Thank you for your responses. Illauna, what exactly do you mean by "big screen mode?" I only know of one screen mode, the default one. How do I check if my sound card is causing it? Thanks in advance.

In Settings-->Interface-->check BigPicture Modus, that makes Steam appear like Windows Media Center....

Although I don't understand why you want to keep that app running when your machine is idleing...? Simply kill it and only start it when you absolutely have to, like starting a game....

Otherwise Steam uses your bandwith to download ads and uses RAM for no apparent good...