What exactly does glEnableVertexAttribArray do?

I have been reading: https://nicolbolas.github.io/oldtut/Basics/Tut01%20Dissecting%20Display.html

Then please read the next page; I explain exactly what it does there ;)

If I may quote myself:

We assigned the attribute index of the position attribute to 0 in the vertex shader, so the call to glEnableVertexAttribArray(0) enables the attribute index for the position attribute. ... If the attribute is not enabled, it will not be used during rendering.

It's similar to a vertex array but stores additional extra values for each point rather than it's coordinates. You might want to store a temperature, density, signal strength at each point in a modelling app for example, or perhaps a damage value for a game