Activity-chaining into a subprocess activity(Configuring the subsequent activity)

Hi,everyone

I have a question.

I check this reference  link:

docs.appian.com/.../Sub-Process_Activity.html

I cannot understand this point.(plz check my screenshot).

Here is my code 

As my imagine when click submit button the next interface will appear subsequently because i checked Enable activity-chaining into all initial nodes in the subprocess

but next interface will not appear subsequently.So my question is the purpose of using Enable activity-chaining into all initial nodes in the subprocess check box and  example how to use that option

Thanks