Sencha Extjs What is the use of Ext.beforeLoad in index.html

In Extjs we have  Ext.beforeLoad  method in sencha cmd generated file index.html.

We have to know what is the purpose of Ext.beforeLoad.

This function is called by the Microloader after it has performed basic device detection. The results are provides in the tags object are.

android: 0

androidstock: 11

bada: 0

blackberry: 0

chrome: 0

chromeios: 0

chromemobile: 0

chromeos: 0

cordova: false

desktop: true

dolfin: 0

edge: 0

firefox: 0

ie: 0

ie8: 0

ie8m: 0

ie8p: 0

ie9: 0

ie9m: 0

ie9p: 0

ie10: 0

ie10m: 0

ie10p: 0

ie11: 0

ie11m: 0

ie11p: 0

ie12: 0

ie12m: 0

ie12p: 0

ios: 0

ipad: 0

iphone: 0

ipod: 0

linux: 0

mac: true

opera: 0

phone: false

phonegap: false

rimtablet: 0

safari: 11

silk: 0

tablet: false

tizen: 0

touch: undefined

webos: 0

webosbrowser: 0

webview: false

windows: 0

windowsphone: 0

         use these tags here or even add custom tags. These can be used by platform
        filters in your manifest or by platformConfig expressions in your app.

Ext.beforeLoad = function (tags) {

            var s = location.search,

                profile;

            if (s.match(/\bclassic\b/)) {

                profile = 'classic';

            }

            else if (s.match(/\bmodern\b/)) {

                profile = 'modern';

            }

            else {

                profile = tags.desktop ? 'classic' : 'modern';

                //profile = tags.phone ? 'modern' : 'classic';

            }

            Ext.manifest = profile;

        };