Take it when your collection is Canoptek-heavy (Wraiths especially) and you want a durable, objective-controlling midboard army rather than a gunline. It excels on Take-and-Hold board control while still killing hard targets through Cynosure, and it's one of the stronger Necron detachments. At 3 DP it uses your whole budget and can't take a support.
Sample gameplan: Infiltrate Wraiths (Dimensional Sanctum) and Scarabs to contest No Man's Land turn one so it flips into your Matrix for full Hit re-rolls. Advance Wraiths and Doomstalkers to hold the middle; when you need a kill, stack Cynosure of Eradication (Devastating Wounds) and Solar Pulse (Ignores Cover). On defence, use Reactive Subroutines to reposition, Countertemporal Shift to blunt shooting, and Suboptimal Facade before a charge. Grind them off objectives while a Reanimator keeps your board presence topped up.