Haven tactics.

Why would you do that? It's fine if you're playing on Recruit or Warrior difficulty. But if you're on Veteran or Hero, you definitely shouldn't do it, as it will ruin your entire development. Maybe it's acceptable if an evil Warlock is heading towards your Castle on the second week, in which case upgrading a few peasants to archers might help you survive. Otherwise, I don't see any other good reasons to do it.