How does Animation Canceling work? Is it a valid technique?

Animation canceling is pretty important in Dota 2. It serves several purposes such as last hitting better, optimizing the time an enemy is stun by one of your spell, or the most important thing in my opinion: Orb Walking. Orb walking consists roughly in moving toward your target as soon as the damage is dealt (either you are melee or range doesn't matter): thus animation canceling in order to reduce the gap between you and the target. By managing this you will avoid the enemy running away because your hero has to stop moving when he attacks: See in this video how drow keeps up with vengeful spirits.

You can animation cancel in 3 situations:

• After an attack: Each hero in the game has a different timing for animation canceling. You have to learn for your character when the attack animation begins, and when the damage is actually dealt to your target. It's easier to tell for ranged heroes as you can cancel the animation when the projectile goes.
• After a spell: You have here to learn when the spell actually starts (or when the damage is done) before animation canceling. One of the biggest examples is crystal maiden's frostbye. You can animation cancel when you see that the enemy stopped moving, if you waited for the whole animation you would have about 1 second less to attack him while frozen.
• During a spell that has an obvious and quite long animation (Leshrac's Split Earth, Eartshaker's fissure, Magnus' Reverse Polarity, etc.). By pressing the "Stop" key during the animation, you can fake the cast of a spell thus baiting a defensive response from your opponents. The spell won't be actually cast saving you the mana and the cooldown but it can bait a blink, Puck's phase shift, or if you are lucky, a Black King Bar use.

You can animation cancel:

• After an attack by moving (easiest way to achieve it)
• After a spell by moving or pressing the "Stop" key (be careful to not cancel your spell, it's more important that your spell hit than animation canceling). In some circumstances casting another spell will animation cancel to. With Crystal Maiden's Frosbyte, you'll be able to cast Frost Nova as soon as the enemy stopped moving thus animation canceling the end of Frostbyte cast.
• During a spell animation in order to bait: only by pressing the "Stop" key. If you try to animation cancel a Fissure by moving you will cast your Fissure first.

It is an excellent technique however it requires a lot of practice. You don't have to think about it when you play but do it automatically. Train yourself with the character you are the most confident with, only practice will really teach you this mechanic of the game.

DotaCinema made a pretty good video that shows the concept more precisely: