Well, Mandarin is the standard spoken Chinese language. And when Chinese people from different regions talk together, they could use Mandarin as the bridge of communication. I mean, for instance, for instance, when a Chinese from Ningbo, a city in Zhejiang, an eastern province in China, talks to a Chinese from Shantou, a city in Guangdong, a southern province in China, they could use Mandarin to communicate with each other.
Here is a video on Youtube in which the Ningbo dialect was spoken.
Here is a video on Youtube in which the Teochew dialect was spoken. Local residents in Shantou speak Teochew dialect.
In a vast country like China, it needs a standard spoken language to help people from different regions to communicate. And this does not diminish the importance of dialects. I mean, for lots of our folks, hometown dialects speak volumes about where they are from and which regional cultures that they represent. When they speak their own dialects, they feel more connected with hometowns where they were born and raised.