In my old 2E group, pretty much everyone always played their own characters. If someone was missing for one reason or another, and the party needed that particular character (or level/class), then they were pretty much out of luck unless the DM allowed them to hire an NPC somewhere.
We did try it a couple of times, but our main thing was that each of us had such different personalities in our characters it was not unusual for someone to end up doing things that were totally out of character for that the "off" character they were playing. That's when we stopped with playing anything but our own.
In my current PF group, the DM doesn't allow the playing of each other's characters at all, which I totally agree with. Definitely less heartache of something goes terribly wrong.