Max-Width vs Spacing tool

Could someone explain the differences?

Just discovered MaxWidth! Why would I no use it on EVERYPAGE?

Spacing tool is for padding and margins on four sides of your content if you so choose. That being said the max-width constrains your content horizontally in the browser window. It is a better, simpler tool for the layout of your content in conjunction with the Spacing tool.

I encourage you to watch the series of videos by RW Classroom. He rebuilds a page from the starter kit