Wat this mean? It means you can force flyers to pass safely overhead and not shoot at your army. Except for Heldrakes, that is. This won't work at all against those, but we're not talking about them right now. Before, you could never truly be safe from flyers because they could usually find a place to deep strike behind you. No longer. Observe this handy dandy diagram I made.
Green = Your Own Board Edge
The red and green fields are areas that flyers cannot reach when they enter the board. By occupying the yellow ellipse with a strong bias toward your opponent's board edge, you force any flyers entering the board to either pass overhead, or fly up the flanks. Either way, they can't shoot at your army as long as you hold the center. I should make it clear that that upper edge of the yellow ellipse is the important part because that's where you're forcing a flyover from. Use your reserves to fill it out.
Daemons are uniquely abilified to accomplish this due to their deep strikeyness, and the fact that Screamers can turboboost a million inches to spread out. Seeker Chariots are also excellent for taking up space. So, if you go first, you're going to have time to get a lot of models into position before any flyers enter the board. If you go second, you just get closer to the opposing board edge so none of your stuffs can get shotted.
If you have flying monstrous creatures, you get free shots against rear armor as a bonus.
Losing deep strike has essentially made fighting the Necron Air Force a board denial game that you should be able to easily win because they simply won't be able to shoot you very much whilst you plink away at them.
Still gotta watch out for Wraiths.