Supreme

Microsoft recommends that you always use a seperate account to install applications and that even your user credentials should not be a part of the Domain Administrators group. Also remember that when you use a SMSAdmin account it is installed under that service accounts security context. So if the user that installed SCCM is disabled/removed it will keep a clean install. The SMSAdmin account is part of the BUILTIN/Administrators group in these instructions. You could do it either way but i think he wants to present the instructions from a "best practices" standpoint. And yes you should use seperate a Domain Admin from your user account...but who does that.