I find that at the beginning of the event the host supplies the drinks. But, as the night wears on and people start drinking more, including the host, it often becomes a free for all. I have no problems when my guests help themselves. I would hate for them to go without a drink due to my lack of attentiveness.
One time we had people over though and they said they wanted to see the kids bedroom and went upstairs before I could stop them or run up first and close the door to our own embarrassingly untidy bedroom. I mean the place looked bad. Who runs upstairs though!! I wasn't prepared, I only deal with downstairs when creating a fake representation of how we actually live ...