Death Knight Haste,Main Uses for Haste

By magically increasing the speed at which a body generates vital energy, the caster may bestow great speed to any being. All actions by one so enchanted are swifter than a common adversary - an advantage that is evident on the battlefield. The effects of Haste can persist for but a short time.

Haste has limited uses. Haste speeds up attacks on only Dragons and speeds up the walking speed of only some units. It speeds up casting of Death and Decay for Death Knights and makes them travel very fast. It also is good for speeding up Peons harvesting Lumber, repairing buildings, and mining Gold. The main uses for Haste are for casting it on Death Knights, Dragons and Peons.

Speed
Haste increases the speed of most units, however, there are some units that Haste does not affect.

Attacks
Haste does not noticeably increase attack speed or the number of attacks except in the case of Dragons. Haste makes it appear through the animation, that units are attacking faster but actually they are not.

Dragons & Gryphons are the only exception to this. Dragons do about double the attacks with Haste on them. Haste also speeds up Dragons even though they are speed 14 to 20+. Hasted Dragons attack faster and fly faster.

There are a few units which Haste has no effect on such as Ogres, Flying Machines, Oil Tankers, Transports, and Destroyers. It doesn't make them travel faster nor attack faster.

Speed of units when Haste is cast

Land
Peon/Peasant = 13 (Same as Ogre)
Grunt/Footman = 13 (Same as Ogre)
Axe thrower/Archer = 13 (Same as Ogre)
Ogres/Knights = no effect
Catapult/Ballista = 9 (Slower than a Grunt, Faster than a Mage/DK)
Sappers/Demos = Speed 17! (Same as Goblin Zeppelin)
Death Knights = Speed 17! (Same is Goblin Zeppelin)
Mage = Speed 13. So Hasted Death Knights are faster than Hasted Mages.

Air
Zeppelins/Flying Machines = no effect
Dragons/Gryphons = Faster than speed 17, about 21+ speed.

Sea
Tankers = no effect
Transports = no effect
Destroyers = no effect
Juggernaughts/Battleships = Speed 10 (Same as Oil Tanker, Transport, Destroyers)
Subs = Speed 10 (Same as tanker, trans, destroyers)

Death Knights
When you cast Haste on Death Knights they move as fast as Goblin Zeppelins and they are able to cast Death and Decay VERY fast. One of the problems with Death and Decay is that often enemy units can simply walk out of the damage area of Death and Decay before they are hit with serious damage. When Hasted, Death Knights can quickly start Death and Decay bringing it to full damage before the enemy units can move out the way.

Dragons/Gryphons
Haste not only make Dragons travel unbelievably fast but also doubles their attacks. Bloodlust a Hasted Dragon to get even more damage. Hasted/Bloodlusted Dragons can destroy buildings and units very quickly but they can still die easily to Blizzards and Polymorph.

Peons/Peasants
They move as fast as an Ogre and are able to repair, chop, and mine much faster. They do not however build buildings any faster with Haste on them except when repair-building the buildings.

Mining Gold
Hasting Peons mining is pretty much useless. It only lasts about 2-3 trips.

Harvesting Lumber
It might be useful to cast Haste on peons chopping Lumber. A Hasted Peon can chop about 200 wood to every 100 that a un-Hasted Peon chops. So it's a 2:1 ratio. Cast it on 4 Peons and you get Lumber fast. Cast it on 8 and you get even more.

Repairing buildings
Haste allows Peasants repairing to greatly speed up the process of repair-building and normal repairs.