[PHP] Self-Process php forms or not?

[MEM]

I’m trying to understand the advantages behind opting by using a
Self-Process PHP Form, instead of having a form and then point the action of
the form to another .php page. 
 
Can anyone point me some resources about this. Why using one instead of
another. What are the main advantages?
 
 
 
Regards,
Márcio