One of the major advantages of being explicit about the meaning of changes, is that you can detect conflicting changes with more precision. Typically, these conflicting changes occur when two users are acting on the same data (nearly) simultaneously. Imagine two users, both looking at a specific version of the data. They both decide to make a change to that data. They will both send a command like "on version X of this aggregate, do that", where X is the expected version of the aggregate. One of them will have the changes actually applied to the expected version. The other user won't.