It's still possible to create a local guest account, but that means giving up a lot of settings that I might want to maintain on the regular account, and it's a hassle to have to log out and in again just because I don't want to record something. Maybe I want to plan a surprise trip for someone who also uses the computer or get information about a strange rash that might be nothing without making that part of my permanent record. Maybe I want to let someone else use software which requires an account, like edit a file on Adobe CS or fix a bug inside Visual Studio, without having everything they do become part of my profile.