The full fuel-conservation strategy across the Apollo mission:
- Translunar injection (TLI): one large burn to leave Earth orbit and start the coast.
- Midcourse correction: a tiny burn to fix trajectory errors, not to steer continuously.
- Lunar orbit insertion (LOI): a small burn, because the Moon's gravity already bent the path into a bound trajectory.
- Transearth injection (TEI): a timed burn that uses the Moon's orbital velocity to help send the spacecraft home.
- Propellant reserve: enough propellant is held back for TEI before LOI is committed, because without the return burn the crew cannot come home.
Across the whole mission, gravity does the large-scale work — decelerating the spacecraft on the way out, capturing it at the Moon, and bringing it back — while the engine is used only for small, precisely timed corrections.