Apple (and Google) blocks all sorts of apps from their stores that even though legal in nature are not allowed for some arbitrary reason that helps their bottomline. E.g. things like gambling, crypto, adult etc are all blocked. On Android you have the choice to side load them on iOS you can't. For this reason alone allowing sideloading will be a generally good thing.

For the average user there will be zero impact and for the power users who wants to still to Apple's guidelines no one is forcing them to install anything they don't want to. If its any similar to Android it will take quite a few clicks to allow the installation which deters the average user from installing unwanted stuff.