[cxr]

You have misunderstood the question. Chrome already allows you to "install" these things today. This post is about a change to Chrome's installation UI. Chrome's installation UI will support the "screenshots" property in the installation manifest now.

When the person you are responding to writes, "What user problem is being solved by this?" they are not being asked to have the value proposition of "installable" Web apps explained to them. They are asking about exactly what they say they are: "Why do I need a screenshot of the "app" (i.e. webpage) I am already using?"