When (as a full member) you've written a long, detailed and hopefully helpful response to a question, hit 'post' and been told 'Sorry - you need to log in as a full member'. Then find you've been logged out and your post has gone awol. Grrrrr.
Are you saying that a session will automatically end (ie. you'll get logged out) after a certain time unless you tick the box? I'll do that in future.
Thinking about it later I concluded that my internet connection might have failed briefly, (it can disconnect and reconnect without you noticing), hence the log-out.
Thanks for the tip.