Subforums are subforums as if they where not subforums the listing of forums would be quite long. The main forums are there for listed and then forums that are somewhat a part of the main category but not really alot of traffic as compared to the main forums are made sub forums of those main so the topics can be centeralized for a given subject mater like cichlids for example but the planted aquascaping discussion does not fully qualify as a main forum.
In addition this site is intended for the all around hobbists and those whom may specialize or wish to focus on planted aquascaping may find themselves drawn more to a planted specific website.
Subforums allow us to keep the pages looking what we consiter good and less cluttered while at the same time having links to the more specialized forums. In total we have 90+ forums including the subforums. On the forum index page we have 28 or 29 forums depending on whom you are listed as main forums. If every forum was listed the page would load 3 times slow and be 3 times longer.