Why is the national party/nomination convention important for democracy in the United States?

What will be an ideal response?

An ideal response will:
1, Explain that the national party/nomination convention is where the party platform is created and the presidential candidate is nominated by state delegates.
2, Note that the current system uses the convention as a way to mobilize party supporters more than as a forum to deliberate on the nominee, who likely has already been determined.
3, Indicate that party platform is a set of durable guidelines to steer the party until the next convention and infer that platforms give voters a sense of what the candidates believe in and the issues they think are important for the country to address.