Why blackout days? What are they for?
The Disneyland blackout days are days some annual pass holders cannot get admission to the park by using the annual pass. The pass holder would need to pay full admission price to enter the park. These are usually the high park attendance days such as holidays, weekends, and now the whole summer of 2019.
The purpose of the blackout days are crowd control, and revenue enhancement - it is better from Disney’s point of view to fill the park with people paying full admission price.
Disneyland has a tiered pricing structure for annual passes. The most expensive annual pass, $1399.00 per year, does not have any blackout dates. The lower cost passholders do have a tiered level of blackout dates.
https://disneyland.disney.go.com/passes/