There is a trade-off here. Yes, some apps might not be available in the main store. Not all of the rules that are applied to app submissions are in the best interests of every user. Even some of the rules that do protect some users, also eliminate whole classes of apps that other users would like to use.
This dynamic is already at play on Android. The lack of Fortnite availability on the Play Store is probably to the detriment of users. However, the existence of fdroid has allowed quite a few apps that users want but that fundementally don't work within the Play Store rules.
So when you ask "What does this do for me as a user", the answer is: it creates the opportunity for you to have access to a more diverse set of apps that are currently prohibited (such as anything with adult content).
Edit: A hopeful secondary effect is that Apple will be incentivized to improve the App Store to compete with third party stores. Maybe Apple will add free trials for one-time purchase apps. Maybe Apple will create an adult content section. Maybe Apple will provide better transparency around rejections. Maybe a store will emerge that does a much more stringent security review that catches the bad actors that do get their apps through Apple's screening. Most likely, none of this will happen and 3rd party stores will see minimal use, predominantly by technical users who want apps that fundamentally violate the store rules, like has happened on Android.
This dynamic is already at play on Android. The lack of Fortnite availability on the Play Store is probably to the detriment of users. However, the existence of fdroid has allowed quite a few apps that users want but that fundementally don't work within the Play Store rules.
So when you ask "What does this do for me as a user", the answer is: it creates the opportunity for you to have access to a more diverse set of apps that are currently prohibited (such as anything with adult content).
Edit: A hopeful secondary effect is that Apple will be incentivized to improve the App Store to compete with third party stores. Maybe Apple will add free trials for one-time purchase apps. Maybe Apple will create an adult content section. Maybe Apple will provide better transparency around rejections. Maybe a store will emerge that does a much more stringent security review that catches the bad actors that do get their apps through Apple's screening. Most likely, none of this will happen and 3rd party stores will see minimal use, predominantly by technical users who want apps that fundamentally violate the store rules, like has happened on Android.