Question: Why Edge Split doesn't dynamically apply its functions through animation?

Using it as a tool (Mesh->Edges->Edge Split) allows you to manipulate each face independently. However Edge Split modifier doesn't work like that. Yes it still increase vertex count but doesn't actually split geometry, unless click *Apply* button.

**Setup:**

**1.** Hook is binded to the top face with Sharp edge surrounding

**2.** Split Edge modifier is splitting top face

[![enter image description here](https://i.stack.imgur.com/GJMii.png)](https://i.stack.imgur.com/GJMii.png)

**Now animated hook is trying to move it:** There is no visible split.
[![enter image description here](https://i.stack.imgur.com/p44lc.gif)](https://i.stack.imgur.com/p44lc.gif)

**After pressing** *Apply* **in Edge Split modifer:** Whole different picture
[![enter image description here](https://i.stack.imgur.com/r3VCz.gif)](https://i.stack.imgur.com/r3VCz.gif)

[![](https://blend-exchange.giantcowfilms.com/embedImage.png?bid=4025)](https://blend-exchange.giantcowfilms.com/b/4025/)

Answer: 
> 
> so why it splits edges and at the same time keeps them connected
>  before applying?
> 
> 
> 

Edge split modifier actually split geometry. But you test this using wrong way. Try to add Susurf after Edge Split:

[![enter image description here](https://i.stack.imgur.com/JUrWv.png)](https://i.stack.imgur.com/JUrWv.png)

When you adding hooks it moves both arrays of vertex, that splitted by edge split modifier
Yes, I understood your problem but i suggest you to split the only desired face by this method:

1:Select
[![Step 1 Select](https://i.stack.imgur.com/avO1Z.png)](https://i.stack.imgur.com/avO1Z.png)

2:Press Ctrl+E

[![enter image description here](https://i.stack.imgur.com/1K2q1.png)](https://i.stack.imgur.com/1K2q1.png)

3: Click on Edge Split

[![enter image description here](https://i.stack.imgur.com/vryR8.png)](https://i.stack.imgur.com/vryR8.png)

And the results would be much better. By this only your desired face will be splitted as it also does not cause increase in unwanted geometery...