Someone Explain "Footdar" to me?

I kinda get what footdar is, sorta... but I don't get the appeal.

How does footdar perform? Why is it a thing now?

It's always been a 5th ed meta army. You take 2 farseers, some wraithlords and a bunch of infantry. You have one strong counterassault unit if the enemy gets too close (banshees or harlequins) and the wraithlords can tarpit. It lost a bunch of appeal when DE came out and toughness 8 became basically useless. But against armies with no poison, it can still be a headache to deal with. It's strong against Grey Knights (because of the presence of Eldrad) and probably pretty strong against most Necron builds, so maybe that's why it has some heat again.