The reserve

Your action points go into a store. The more land you hold, the bigger the store.

The slider Keep for defence keeps part of the store at home to protect your land. Only the rest goes into your next wave.

Keeping more makes you safer, but you grow more slowly.

Defence
Points you keep guard your land. Send everything and you are easy to take. Each piece of land you lose costs you points. Only with a watchtower of the map: for an enemy with land in its range, the shields over his land and the list of neighbours tell what your attack would bring, with the share of his land: "Strong attack" takes 25% of his land or more, "Weak attack" less than 5%, "Fair attack" lies between. It counts the points a click would send right now and the points your running wave was given. The more points he keeps, the less you take.