The split is persona/use-case based.
Dashboard embedding should be enough for people who consume dashboard content.
• For users who are explorers by nature, GD provides ability to explore dashboard content further using “Explore from here”
• For users who would like to create their own dashboard, GD provides ability to do so from the dashboard - again using an embedded analytics designer. This embedded experience does not provide all the features of a fully-embedded analytics designer - specifically users cannot create new MAQL metrics.
Analytics designer main focus is ad-hoc analysis. If you want to provide your customers just this use case, then embed a separate analytics designer.