ExtJS 3.x vs 4.2.1

Hello,

I am fairly used to version 3.x and I am now getting back at it almost 4 years later

I see there's, what seems to me to be a new concept, the "Application". Generated with its dependencies, models, stores, etc.

I tried going at it the old fashioned way, which is basically including the basic .js file of the SDK, creating an Ext.onReady method and rendering controls to DOM elements within my HTML page.

I am getting weird errors, but for the moment, my question is not about the errors, but rather whether I absolutely need to use SenchaCmd and use this "application" concept for it to load and work correctly.

It's been quite a while since last time I used ExtJS, so I'm wondering if a lot of concepts and best practices changed since...