The democratic leadership style actively involves the citizens into policy-making.
The Advantage of this is the fairness of the system, and the fact that all the fractions will be represented, and at least theoretically no part of the society will be neglected (in non-democratic rule, it could happen that some parts of the society are heavily discriminated against).
A disadvantage is a relatively high cost of referendums and elections, and the slow character of introducing new laws.