Tomb Blades are the Necrons' obligatory jetbike unit. They were invented during the War in Heaven as spacecraft -- as the Necrons no longer breathed, they had no need for space suits or enclosed cockpits. They turned out to be extremely effective in atmosphere as well, and so they also became part of the Necrons' ground forces.
They are flown by Warriors, but because Warriors are terrible pilots on their own (being incapable of independent thought), the Warriors are themselves governed by "a series of hyper-fractal equations" that constrain the Tomb Blades to preplanned attack patterns. Why the Necrons bothered with the Warriors is a mystery for the ages - although the book Hammer & Anvil implies its for the Warrior's auto-repair abilities.
Since deploying starship-grade weapons on the same continent as other Necron forces would be dangerous and self-destructive, ground-bound Tomb Blades are fitted with infantry weapons -- most commonly, a twin-linked set of gauss blasters or tesla carbines, although it can also use a Particle Beamer.
On the Tabletop
On the tabletop when they were first introduced, the Tomb Blades were initially used as a quick Line Breaker unit and thus, didn’t see a ton of table top usage as they were kind of redundant, what with the basic Necron foot soldier already considered a Line Breaker of sorts. However this all changed when the new book hit and they got a significant boost in the power department with decent toughness, strong shooting, and a plethora of good rules. And when we meant decent, we mean cheesemongering bullshit sandwich, we are talking about extremely fast and small jetbikes that has weapons that is either Twin Linked and ignores cover which can quickly amassed into Str 5 weapons and allows them to Wound/Glance on a 6+ versus anything which makes most Xenos armies to bend over and cry as they normally do not get the 3+ armor you see in Marines and other Marine like armies. To a weapon that shoots a Str 6 Ap 5 small blast that also Ignores Cover as well and add in a ton of wounds.
But wait! There's more! Just when you thought the brutal raping would end there is the Tomb Blade's special rules. Just like all Necrons they get a Reanimation protocol save. This unit is part of the basic Decurion so they can get an improved save as well as Move Through Cover. Furthermore they can get +1 cover save through the Shadowloom upgrade as well and as a Jetbike they are extremely fast and give a Necron player a massive mobility advantage in a ridiculous buffed up army. The 3+ armor save upgrade just further seals the deal. Also as this is a Jetbike unit they get +1 to their toughness making small arms fire have to work a lot harder to wound them. So unless if you're a Guard or Spess Mehreen or a Chaos player, you are not going to have a swell time when these units come to battlefield. Special prayers are held to Dark Eldar players whose entire army might as well be weeds to be harvested by the Tomb Blades.