google cloud platform – GCP Pubsub Subscription Write to bigquery – using topic schema vs table schema

Exploring to load the data from pubsub topic to Bigquery table using the Subscription type ‘Write to Bigquery’. While configuring the subscription, there are 2 options: Use topic schema and Use table schema. Trying to understand the difference between the two options. Gone through the official documentation but could not understand it.

Topic schema: The message definition and the table column names should match. The data from the message will be loaded to the table.

Table schema: same as above???

Can someone please explain it in easier terms.