yeah its similar with other games...
best example - Enemy Territory.
while the basic install is only 250 MB it can grow like nothing.
before i cleaned up last time it had well over 6 GB... (maps, mods ect...).
in lfs the skins make the most size, although one piece may not be big, thousands of them can be.
i deleted one time my skins_x folder (well, the files inside) and cleaned up almost 1,5 GB that way...
not even talking about all the addons that are availble.