When an email tool is properly connected to Shopify, it receives far more than an address list. It gets order history, product and collection data, cart and checkout events, browsing behaviour, customer lifetime value and, if you sell subscriptions, renewal dates.
That is the raw material for every useful piece of segmentation. Buyers of one category versus another. First-time versus repeat. High spenders. People whose consumable is due for reorder. People who bought the thing you are about to discontinue.
Most stores never use it because the connection was made once, at launch, by whoever set the theme up, and nobody has looked at it since. The first thing I do in a Shopify account is check what data is genuinely flowing, not what the integration screen claims.