Combining flex shorthand with percentage width?

The SUITCSS size utilities combine flex shorthand with percentage width into u-sizeXofY utilities.

Here's is a link to the tests.

The flex property is set like this:

flex: 0 0 100%;

And it's combined with u-sizeXofY utilities like this:

 width: 50% !important;

What I'm trying to understand is why they are doing that?

What is the reason for combining flex: 0 0 100% with the width: 50% !important; utility?