Booster car seats are the next phase in car seats after the forward-facing stage when your child outgrows a convertible or forward-facing only seat. They are essentially combination seats without the forward-facing configuration. You can only use them in booster configurations. Best practices indicates that after rear-facing, you should forward-face harness until children reach the weight or height limits in the forward-facing position and are mature enough to use boosters, which is ideally no earlier than 8. The drawbacks of booster seats is that they aren’t as versatile as combination seats.