What does the Harpy's first-turn effect that lowers combat level to 0 actually do?

Question

Accepted Answer

It lowers the Witcher's combat level to 0 only during the first fight turn, so you draw no cards from your combat level that turn (modifiers in your combo may still change the count). It is back to normal from the second fight turn.

The Witcher: Old World

What does the Harpy's first-turn effect that lowers combat level to 0 actually do?