More details required for [EXTRA_STEP] section

Hi, I have a couple of questions for [Extra_step*] section:
1). What's the different between [step*] and [Extra_steps*]?
2). Why not just use [Step 1,2,3....n] since they are all about submission process?
3). Could you please show me samples and situations when the [Extra_step*] should be used?

Thanks again for your help, @sven.