Why use Atlaskit Page Layout RightPanel instead of flexbox with RightSidePanel?

[uidev]

I'm struggling to understand the value page layout provides or why it's a recommended best practice?:

https://atlassian.design/components/page-layout/examples#integrated

From what I can tell, the width of each section is a `prop` determined in pixels, but what if you want a flexible and seamless layout where everything scales with screen size and you instead want to set a flex-basis in percent rather than absolute pixels?

For instance, I've found using simple divs with flexbox layout is powerful because I can set relative ratios each section of the page should have, without much extra typing than I would have to do using Grid, or GridColumn (and less dependencies!). But then on the side that means I'm using the alternative, `@atlaskit/right-side-panel`, inside my div rather than using the built-in `RightPanel` component that comes with `@atlaskit/page-layout`. What's the difference and why does `RightSidePanel` exist if there's already `RightPanel`?

Just making sure I'm not reinventing wheels and using Atlaskit as intended. Also, heads up the docs have some G-rated profanity I don't think were added on purpose!:
https://atlassian.design/components/page-layout/examples#using-css-variables