Need comprehensive instructions for POP setting 'Delete emails on server'

Need comprehensive instructions for POP setting 'Delete emails on server'

Hello, I have set Delete emails on server and my mail is now all going to trash.  There are two problems here:
1.  I am unable to find where that setting is.  Do I find it in mail.zoho.com or mailadmin.zoho.com?  I think that I and many other users would appreciate some screenshots for finding the actual place to set it, because it seems to be a common problem.
2.  There should be help explanation / or warning against that setting when configuring it because the results are somewhat damaging to the mail experience.  Why have it at all?

Thanks in advance for your help.