What's advantage of increasing numThreads of RDB async-executor?

Hi, I saw this default value of DB async-executor.
And the sample (default) value of numThreads is 5 times of number of core

I guess the core is the number of cores of my host machine.

If my host has 8 cores, and increase it to 5*8=40, can I expect better performance?

And why is it saying I can put 5 times of my core?

  async-executor {
    # number of objects that can be queued by the async executor
    queueSize = 10000

    # 5 * number of cores
    numThreads = 20

    # same as number of threads
    minConnections = 20

    # same as number of threads
    maxConnections = 20

    # if true, a Mbean for AsyncExecutor will be registered
    registerMbeans = false