[huehehue]

My current company's CEO is a bit of an icon in the startup world, and his fans can be...intense. If we leave the office door unlocked during work hours, people can (and have) just waltzed in hoping to meet him. People also send all sorts of weird gifts.

Since we were basically working out of a house for the longest time, whoever was on hand would have to deal with the unwanted guest. If you're alone in the office and some big dude comes in saying "Well I won't leave until I meet your founder!", that can be scary.

As Gustomaximus puts it, it is to keep potential lunatics away.