Nature Structures

Nature calls rarely, and even then, only low-level monsters appear. Haven, on the other hand, can replenish its ranks with titans and dragons if you're lucky, and even a weakly developed Charm skill is very helpful in the early game.
Although comparing these two characteristics is not entirely accurate, Charm is more comparable to Necromancy or Diplomacy. Summoning is a separate ability, and in my opinion, it is only effective with artifacts (50% + 50%), such as the amulet with the beetle and the staff.

Unfortunately, Charm is not very useful. Even if you're lucky enough to summon titans and dragons, which is unlikely, you still need to level it up, just like Summoning. So, what's the point? You have to level up either one or the other... Again, I'll reiterate the problem with morale, which can be negatively affected by dark factions (Chaos, Death, and Strength, I think). So, Charm can even be detrimental at times, and is generally useless (when compared to Summoning). The only advantage is that it slightly reduces the enemy's ranks.