What's with getting autologged off?

[David]

How come this happens all the time? I spend a few minutes writing a post & by the time I go to post it, I've been autologged off, which forces me to hit the Back button, copy my entire reply to my clipboard (or lose it all), & then re-log on again, go back to the forum I was at & repost everything.

pain in the arse ... what's the purpose of it? Is it a moneysaving device?