You often see ("often" depends on your point of view) relatively long (also depends on your point of view ;-)) post with short updates like "changed ~= to =~, thanks to ...". If you store every instance of the node, the data would grow pretty quickly. Maybe diff would be a soulution, but I think there's always the problem with the available disk space.
Cheers,
CombatSquirrel.

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Entropy is the tendency of everything going to hell.