Time for some simple roleplaying.  As I said before, chanties should really only be used when the enemy scout is dead, or to capture the enemy scout.  I also try to kill witches and pyros early, but their range is much more limited than a scout, so that's not as critical.  In all the screenshots, the intelligent chanty user is always in red, and I'll try to use blue for the enemies.  Is it just me, or do red bikinis always just look soooo hot?  I want my chanty looking sexy for the photoshoot!  In this scenario, the enemy is making a 2 unit rush into our backfield.  From where the scout is, he can hit just about any unit he wants to with minimal movement.  The knight is 1 square out of range from our chanty, and can't get to our cleric, but he can definately hurt us.  Scouts take significant effort to kill, and knights usually live until the end because they're just tanks.  We could blindly attack, but we'll never kill both those units before they can really hurt us. 

Since we can't kill these units, we need another strategy.  Let's bring in our highly underrated enchantress and teach this opponent about her.  She has several places she can move to, as shown in blue in this picture.

In order for her to be effective, we really only have a few options for movement as shown in red in this picture. 

moving to 2 of these squares will paralyze the scout only, while the other 2 will capture both the scout and knight.  One of the squares will also paralyze our barrier ward, which would be very stupid.  This leaves us with 2 options.  Normally, I would prefer moving her towards the front as much as possible, hoping to capture more units who come in to free their comrades, but in this scenario, we'll imagine the enemy is using the default setup, so he has a pyromancer in the position shown.

If the enemy understood the game mechanics well enough, he could charge that pyromancer forward to the position shown after we freeze the knight and scout, and break our focus. 

We'd be in a world of hurt if that happened, but fortunately we read this site, so we know better than to do that.  We'll move to the only real optional spot we have and capture both the scout and knight in 1 freeze.