No. 1: Instead of buying a ticket and showing up next week or next month or next year, you tell Disney when you are going to go to a park. Disney knows those tickets have a shelf-life after you start using them. It offers a bit of advance warning on crowd size.
No. 2: Reserve every park day. This gives Disney the most info, however, it is the most annoying for guests.
Disney wants to know how many people are coming to the parks so it can staff them correctly. No. 1 helps with that while giving more spontaneity to guests.
Disney can also use this to gauge how many people dislike making the daily park reservations. It could be that 99% of the complaints they get about daily reservations are from 1% of guests.
Anyhow, I prefer No. 1