Why do Terran players use the Marine blob micro move?

The benefit of this fancy micro is to 'run and gun'. Marines have a set attack speed, meaning if they are standing still they will shoot, stand still, then shoot again.

So by moving between shots you can constantly be moving away from melee attackers you can kite them (prevent them from hitting you therefore taking far less damage) while still doing the maximum amount of damage (because you shoot every time its off cool down). This becomes even more effective when you mix in mauraders with their concussive (slowing) shells.

To answer your question, this can be extended to ANY ranged unit in the game. It is very common with hellions, thors, marines, and mauraders with Terran

To do this micro, right click away from the enemy unit (ordering a moving command), press the A (attack move command) and left click (this will cause your marines to shoot anything within range) then order another move command; repeat.

Hope this helps!

I think the stutter step is an important technique to master, but an vastly more important technique is splitting your units.

Consider a nice and tight Marine ball using stutter step to run away from a group of banelings. Eventually, one or two will make it.

Now consider, instead, splitting up your marines.

This is a technique that MarineKingPrime (formerly known as Boxer, though not the same player as SlayerS_Boxer) is famous for in his ZvT and lead him to be runner up at GSL2. By quickly splitting his Marines, he was able to mitigate almost all of the splash damage.

The goal here is not to save all of your Marines, but instead to save most of them. It's a technique that was pioneered in Broodwars to deal with Zerglings and Zealots. Given a clump of Marines separate them in sections away from the center. As a result, melee units (which Zerglings and Zealots happen to be) are forced to finish off single clumps before moving on to the next. This additional travel time is gained DPS time. In the case of Banelings, you get the added benefit of less splash damage.

The penalty for screwing up a split is losing only a portion of your Marines, while the penalty for screwing up a Stutter Step is to lose almost all of them.

There are multiple scenarios in which stutter step should be used:

1. Retreating your army: You can do some damage while you run away.
2. Attacking fleeing opponent: You can maximize your damage until your enemy escapes. Usually this is the fastest way to kill the first scouting probe in a game.
3. Attacking through a narrow choke: As you have to go through a choke your concave will be worse. But if you push further into your enemys troops (until they stand right next to each other) more and more units of your own can shoot them. Again you maximize your damage during sliding forward.

There is an optimal move speed. If you move too far you miss some time and your shot gets delayed, which reduces the overall damage. If you move not far enough you miss on movement. If you move too fast after you shoot you cancel the shot and thus reduce your damage.

The execution is as follows: Right click where you want to move (not attack move), press "S" on the perfect timing. Wait for the marines to shoot (start animation), cancel animation with another right click.

It is possible to calculate the effectiveness of your stutter step (e.g. 95% damage). For this you need to take two equal sets of marines (e.g.: 1 and 1) the first set shoots a stationary target. The second set shoots a slow unit (like a queen off creep). Compare the damage dealt to the stationary target with the damage dealt to the moving target after X seconds. If they are equal you do 100% and you have microed your marines perfectly.

QXC created a training map for this: http://www.teamliquid.net/forum/viewmessage.php?topic_id=149218

It also calculates the damage for you, pretty handy.

There are other ways to micro your marines. They have all the same basics, but different intentions.

Splitting: You retreat will your whole army. While retreating you select a subset of your marines and click on another location where they should move. Repeat that with other subsets of marines. Basically you want some of them to stand and shoot while the others move away. So they kill some banelings and if banelings hit then only a few die.

Creating a better concave: You reatreat a bit. While you reatreat you select a subset of your marines and click next to the location where the other marines will run. Repeat this with other subsets. Your goal is to build a (concave or line). This way you have a perfect concave if the enemy units arrive and they clump up.

Running in circles: Suppose it is early game and you have a 2 marines and a zealot attacks. If you stand your ground you die. Split them and select the marine which is targeted by the zealot. Run him around the other marine (Issue a command queue) while he is shooting the zealot. If he targets your other marine just switch the roles. This gets harder the more units are involved.

Focus on single target: If you focus an enemy unit it dies very quickly. This is better than attacking multiple targets and removing half their HP, as still all of them can shoot you. This way you take less overall damage.

Falling back with injured units: This is the "counter" to Focus on single target. If you see one of your units taking damage. Select it and click somewhere (not too far) behind your army. The unit will walk away from the battle with few HP. Another unit will be targeted by your enemy, but your weak unit will return automatically to the battle (this is why you do not click too far away) and attack again. Your overall damage increases.

There are many other techniques, but it would take too long to explain all of them.