Discussion about Sylvan (Wood Elves).

The choice depends on many factors. I usually start building upgrades after all the dwellings are available in my town. In principle, if the main hero or the second hero is Ossir, plus a dwelling on the map nearby, and the map is rich, you can try to upgrade and then run to find wood. :)
On a small map, I wouldn't sacrifice 4 dwellings – you might simply not have enough tanks in a battle.

Hmm... Here's an example of a small map – Former Friends. You probably know that whoever takes the center first has an 80% chance of winning.
On this map, rushers rule – Orcs, Mechanists, Leto.
And it's almost impossible for an Elf to break through to the center early without upgrading archers. And with the upgrade, I buy a Dragon on day 5 or 6. Why should I wait for Ents?
With the dragon, I clear the surroundings and on day 8, I take the second hero. I wait for the opponent and support my army.