Initializing Transactional Replication From Backup

Question

There is an option when setting up a publication for replication to Allow Initialization From Backup. We have been creating replicated databases for several years now and have always initialized from a backkup but have never set this flag (we just noticed it for the first time a couple of days ago). The replication certainly has worked without issue all this time.

I've found a lot of hits explaining that this needs to be used but none that explain why.

Does anyone have an understanding of what this actually does? From my vantage, it doesn't seem to be necessary but I'm thinking I have to be missing something.