Also sisters can be hard, you probably will need real monolith for them, but still saves a lot of time, though it will be hard, because you will need to keep saint from main building far enough, to let your other troops destroy main building, normal play trough as necrons will be painfully long. Same can be done with pretty much all other races, except chaos, them you will be forced to kill as developers intended i.e destroy shrines then destroy main base.

For example tau stronghold, soon as you able transform necron lord into deceiver(need build core and buy upgrade in it) you can finish their stronghold, just create many immortals(out of limit with tomb spiders and resurrection orb from forbidden archive), also from archive give necron lord defensive abilities, like scarabs, solar, and then use his teleportation from relic point(you don't need take relic point), which might not be easy because necron lord will be dropped a lot, which might prevent teleport, but still possible, move him to the main mission objective which u need to destroy(tau coalition center), turn him into deceiver, create false monolith, teleport immortals and regular warriors to false monolith and wipe the building, that's it, mission will be completed. Strongholds is another story, as necrons you can abuse game mechanics. And if it's strong enemy territory, then just hold them on their bases, don't let take map control, while at the same upgrading monolith for T2, and then create immortals and flayed ones to finish enemy. Pretty much the same as with others you attack at the beginning of match with your honor guard units, and since necrons have destroyers as honor guard units it's very easy to wipe enemy territory.

Dawn of war necron units