What exactly keeps my chunks loaded here (pics) ?

[lenscas]

AAAAAh ! Of course, falling through the world ! That always happened to me when crossing into the Twilight Forest. I lost all my stuff, TWICE ! From then on I only used Mystcraft books.

Not sure if that is the real reason. The reason that I have been told is that for servers it could be better for the servers resources to always have them loaded then having to unload and reload every time a new user joins.

Not sure if it is really better for most servers but I am told that that was the thought behind it.