The scenario is when your publication settings has the option
immediate_sync configured as false (means if you run the Snapshot Agent, the snapshot files will be created for the new articles only and also a new subscriber to the existing publication, the snapshot files only get created for the new subscription)
This option immediate_sync will prevent to generate all snapshot files but it still need schema lock to check all articles in the publication.
Continuing with scenario that you have a large number of articles and a bunch of subscribers, you might face the situation you have to add a new article in your transactional replication and after run the snapshot that article is not propagate to the subscribers.
First, check your publication settings.
exec sp_helppublication 'PublicationName' GO
With immediate_sync and allow_anonymous false you can run the procedure below to solve the issue that your new article didn’t propagate to your subscribers.
exec sp_refreshsubscriptions 'PublicationName' GO