Brees will still get the $23 million in cash he's due in 2019, but the simple restructure will push his cap figure higher in 2020, freeing up space to use now.
With Brees entering his age-40 season, the New Orleans brass is attempting to upgrade the roster to make another Super Bowl run. In order to do that it needs wiggle room.
Generally simple restructures like this don't even reach the level of being considered a legitimate news item. NFL teams do them all the time to create cap flexibility while kicking the can down the road.
Brees' current contract he signed last year included a voidable year in 2020 to spread out his signing bonus cap hit on the two-year deal. With the restructure, the Saints will be staring at a $20 million-plus cap number on the quarterback without him even being under contract. If Brees decides to continue playing, the team will have to employ more creative accounting to make the numbers work again next year.