If you are not bringing your own Blockchain endpoint, Workbench will create one instance of Azure Blockchain Service as the underlying Blockchain consortium resource. As configured, the Blockchain will generate block at least every 5 seconds even no contract/transaction is deployed.
See also: Blockchain Metrics
"Processed Blocks: The number of blocks processed in each time interval. Currently the block size is 5 seconds, hence in a minute each node will process 12 blocks and 60 blocks in 5 minutes."