The correct answer to this open question is the following.
Although there are no options attached we can say the following.
If there is rarely a mystery about who will be nominated at a party's national convention, these conventions influence American democracy in that they are traditional political events that are part of the United States politics idiosyncrasy and a true American tradition that is part of the ingrained culture of the country.
These political conventions are something like protocol ceremonies to invest the party's candidate. The event is ceremonious and it is like a ritual that people and party members like to have to feel they are part of something big and that their opinion has heed.
It is a moment in United States politics that exemplify American democracy by the open reception of new ideas that are part of the party's platform and would be part of the political campaign of the candidate during his/her events and debates.