Does a Progressive Web Application Service Worker help to speed up site with multiple database queries?

If I have a website that is a PWA, how does this help me with database results? For example, if I have a list of products or names, doesn't matter, how do Service Workers help me with this? On Google's Dev site it shows:

var networkDataReceived = false;

startSpinner();

// fetch fresh data
var networkUpdate = fetch('/data.json').then(function(response) {
  return response.json();
}).then(function(data) {
  networkDataReceived = true;
  updatePage(data);
});

// fetch cached data
caches.match('/data.json').then(function(response) {
  if (!response) throw Error("No data");
  return response.json();
}).then(function(data) {
  // don't overwrite newer network data
  if (!networkDataReceived) {
    updatePage(data);
  }
}).catch(function() {
  // we didn't get cached data, the network is our last hope:
  return networkUpdate;
}).catch(showErrorMessage).then(stopSpinner());

But what if my results are always different? Someone make lookup cars one minute and the next shirts. I do not understand what a PWA Service Worker can do here other than give the illusion of speed.