Could anyone help me to understand what is it for? And what to submit for this question on the SF-86 form? Thank you
The contact information requested on the security clearance application, home/work emails, home/cell/work phone numbers are for NBIB personnel so they can contact you.
List information where you can be reached by an investigator. Leaving off your personal email and phone numbers can cause a huge delay in your fieldwork if NBIB has to reach you. Unfortunately, personal email and phone numbers are often omitted - then the Subject moves or finds another job rendering the address and work contact information useless.
BI nailed it. So often a person clears and the clearance folks cannot contact them. So we are left calling relatives on the SF86 for them to get in touch with us. If your email changes, call the HR or FSO person to make sure the info is updated.