Session Storage matters because session storage can hold UI state but disappears when the tab closes. It gives builders a precise word for the thing they are changing, debugging, reviewing, or shipping.
ELI5
Think of Session Storage as a named piece of the app screen or browser toolbox. It gives one small job a clear name so the whole app is easier to understand.
In practice
Use it when checking how users interact with the page or how browser code behaves. In practice, name the owner, input, output, failure mode, and proof before relying on Session Storage.