> can someone explain to me the point of the 'initial valuation'

Most of the institutional and retail placements happen on the initial valuation. These are the people who are holding the shares when it gets listed and starts trading, and it is the primary source of raising capital through an IPO.

To go further though the Initial Valuation (usually a range) is set weeks before the IPO to make it easier to pitch to investors. And the final valuation is locked in the night before trading based on actual demand.

The opening price on the stock exchange, though, will be whatever the demand and supply is in pre-market trading/open.