Fools who want to long and short the price of BTC or only come in to make a quick buck no longer have to buy actual bitcoin to do it, if they post orders, then those will go to the ETF provider and the bitcoin price will change only if ETF managers buy or sell their own bitcoins.

Among other things, the amount of hacks will go down dramatically for these users too, as there is no more seed phrase or private key to enter or give away.