Discussion of level 1 monsters.

Pirates are useful, especially on maps that are mostly water. On water, movement isn't affected by the creatures' speed (the army isn't slowed down), and they can move and fight normally. On land, yes, they're like upgraded Rogues, but they're slow. An example of pirates being useful is in the campaign for Taun Balfor – there's some water there, and besides them and the Rogues, there's no other army. And they turn out to be stronger than the Rogues (even on land). Later, as the city develops, they become useless (Rogues also become useless at this point, but they can still be used for "steal-bring-deliver" tasks). Skeletons are a good option. A Necromancer of level 1-2 arrives at a location with Archers/Crossbowmen, casts Poison, puts a Skeleton in front of the hero for defense, and waits for the archers to die. What's wrong with that? And they're not a waste, because the growth rate is good, plus Necromancy and the Transmuter spell. Now imagine that your hero has 3rd-level skills and Teleportation. And a Tactician as a companion. You gather a couple of legions of skeletons from all the cities, teleport, and win. Carrying them around with you is, of course, more trouble than it's worth, and sometimes it's annoying to have to move them to the nearest city with a caravan depot. As for Zombies, it's really unclear what their purpose is. Zombies are probably the most useless; maybe they're meant to be used to poison Djinns and dispel their enchantments, causing fatigue, similar to "skeletons against archers." And in that case, skeletons are also better against Medusas than Trogolodites. But what's the point of Imps in an evolution where they're already weak, and they've been made even weaker by increasing the mana cost of Angels/Devils/Nightmares/Phoenixes to 2, which makes a single unit of Imps simply useless/rarely useful? I don't know.