Cardano is a proof of stake system, so holding stake, i.e. owning ADA, means more than holding Bitcoin means for the Bitcoin protocol.
Cardano is a fully-fledged cryptocurrency, so of course ADA can be used to buy goods or services. In addition to that, holding ADA also comes with the right and obligation to participate in the protocol and to create blocks.
These two aspects of holding ADA can be separated by means of delegation: a stakeholder can delegate her right to protocol participation while retaining the monetary value.