ALLIANCE ANNOUNCEMENTS

I also want to learn how to play Heroes 3. Then they call an allied clan and say: "Guys, we don't have another player for Heroes 3, let Arandor play for us."

Well, it's not quite a good example, let me explain:
If you want to learn how to ride a bicycle, it depends on how Arandor rides for you; you won't learn anything. ;)

In this case, a military alliance isn't needed, but rather joint training... that is, it's necessary for HN to play with Arandor, not for him to play as HN. :)

Well, in general, I understood what Draco meant, especially after the words
QWERTY. And I understand why this is needed for OP and EPU (although I am very much against such a thing as supplementing with players from other clans).

Supplementing (in the literal sense of the word) contradicts the meaning of dividing into clans; it's better to simply merge the clans. :)