The larger the number involved, the better the occasion. For example, John's invited all his family to come along, and why not? The more the merrier. This expression was first recorded in 1530, when it was put as “The more the merrier; the fewer, the better fare” (meaning “with fewer there would be more to eat”), an observation that made its way into numerous proverb collections.

see more the merrier.

The more people there are involved in something, the more fun it will be.