Low End Modular - what is the line next to each macro?

I just Low End Modular this and have found manual sorely lacking - I cannot find the answer to the following question anywhere (hoping you might be able to answer for me):

Next to each "Macro" is a short grey line:

When I click the short grey line it turns into a short white line, until I move the cursor, then it turns into a longer white line:

At first, I assumed it was a power button to turn on each macro but, whether that line is grey or white makes no difference as the macro still effects the sound exactly the same

All of that being said, my question is: Does anyone know what clicking that short grey line does once it turns into the white line?

Thank you