I can not exactly see the point of subclans. While it does enrich training, subclans often suffice only to cause members to become angry at eachother and does not teach cooperation skills. It is always prudent to teach teammates how to cooperate. However, there is very little difference between subclanning and multiclanning. Many clans also do not like challenging subclans, thus the results are not held to be as important as those results of "direct" clanwars. Still, subclans provide a chance to learn how your team mates play. Still, those clans that do not wish to play against subclans aren't "cowards" - they just probably do not wish to do what they see as wasting their time by playing a subclan.

Oh, and by the way, you might as well play as your real clan against any other clan. There is no point in matching subclans versus full clans.

Subclanning is not widely accepted; some consider it multiclanning, and some do not. If you're willing to risk that other clans will consider it multiclanning (which could cause a very slight clan reputation damage incident), multiclanning provides a good training method assuming you play against other subclans within your clan.