If a planet is too small (< 0.07 x Earth's mass), then its force of gravity
is insufficient to hold onto an atmosphere (for example, the Moon).
Active geological processes (especially plate tectonics)
are required to renew the surface and
atmosphere (CO2), and this suggests an
even larger mass (0.25 x Earth's mass) is probably required
for internal heating (or external heating by tidal stresses).
If a planet is too large (> 10 x Earth's mass), then its gravity is strong
enough to retain its original hydrogen atmosphere, and the planet would
become a gas giant (with no solid surface).
Our Moon acts to stabilize Earth's spin axis (avoiding huge climate swings) and creates tides (important in evolution of life from sea to land). The presence of the Moon aided the development of life; whether it was an essential factor is unknown.