@SovietReporter asked a really good question on c/askLemmygrad, and later on I stumbled on a text by Huey Newton that synthesises well the need for a vanguard party, so I decided to share it here for more visibility.

Choice quote from the text:

The relationship between the vanguard party and the masses is a secondary relationship. The relationship between the members of the vanguard party is a primary relationship. It is important that the members of the vanguard group maintain a face-to-face relationship with each other. This is important if the party machinery is to be effective. It is impossible to put together functional party machinery or programs without this direct relationship. The members of the vanguard group should be tested revolutionaries. This will minimize the danger of Uncle Tom informers and opportunists.

The main purpose of a vanguard group should be to raise the consciousness of the masses through educational programs and certain physical activities the party will participate in. The sleeping masses must be bombarded with the correct approach to struggle through the activities of the vanguard party. Therefore, the masses must know that the party exists. The party must use all means available to get this information across to the masses. If the masses do not have knowledge of the party, it will be impossible for the masses to follow the program of the party.