Just to illustrate the impact, assuming that your server is hosted in `us-central1` and it is talking to a service in `us-east1`, just the network latency is ~20ms. Since a TCP handshake is a 3-packet event, this means that ~60ms are going to be allocated just to establish TLS handshake.

You can test that with a simple script:

    const got = require('got');

    const main = async () => {
      const response0 = await got('https://posthog.com/');

      console.log(response0.timings.phases);

      const response1 = await got('https://posthog.com/');

      console.log(response1.timings.phases);
    };

    main();

    {
      wait: 1,
      dns: 20,
      tcp: 72,
      tls: 74,
      request: 0,
      firstByte: 79,
      download: 222,
      total: 468
    }
    {
      wait: 0,
      dns: 1,
      tcp: 67,
      tls: 69,
      request: 1,
      firstByte: 73,
      download: 234,
      total: 445
    }

    const got = require('got');
    const https = require('https');

    https.globalAgent = new https.Agent({ keepAlive:true });

    const main = async () => {
      const response0 = await got('https://posthog.com/');

      console.log(response0.timings.phases);

      const response1 = await got('https://posthog.com/');

      console.log(response1.timings.phases);
    };

    main();

    {
      wait: 1,
      dns: 27,
      tcp: 77,
      tls: 75,
      request: 0,
      firstByte: 75,
      download: 220,
      total: 475
    }
    {
      wait: 0,
      dns: 0,
      tcp: 0,
      tls: 0,
      request: 0,
      firstByte: 77,
      download: 83,
      total: 160
    }

If your application relies on making many HTTPS calls, then simply enabling `keepAlive` is going to result in a significant performance improvement.