jimu layerStructure and layer.hide()/layer.show() - Calls to ArcGIS Server

[Arne_Gelfert]

Working in the world of custom WAB development using JSAPI 3.x, and looking at some performance tweaks.

Notice that when I use the following approach to update multiple layers' visibility, it takes a long time to update the map...

layerStructure.traversal(function(layerNode) {
//...
   layerNode.hide()
//or
   layerNode.show()
//...
})‍‍‍‍‍‍‍

What I see in Chrome Dev Tools is that for each pass through and layer for which visibility is updated, there is a call to server that returns a new PNG. I guess that makes sense. So we're waiting for the last of multiple images to be available before the update of the map is reflected in the browser. Is there a way to somehow redesign this to where I can make all my update before the call to the server happens and then receive one PNG?

On on only remotely related note, it says here ( Feature Layer Best Practices | Guide | ArcGIS API for JavaScript 3.33) that for JSAPI 2.6 and later feature generalization (using maxAllowableOffset) is the default. Does that also apply for any layers in Web AppBuilder? If I have a a webmap that includes a layer with rather complex polygons, is it by default using generalization when zooming in/out, and if not, how can I leverage maxAllowableOffset?

Thanks!