Form 80 is used for security clearance (so far I understand). Typically you need to send it when the CO asked for it. Otherwise don't provide it.
I think they used form 80 and its verification to judge your potential as a security threat. Usually applicants from countries not issuing Machine Readable Passports (MRP) are required to provide the form 80. Though MRP passport holders may require to provide it. For example, we hold MRP, but we had to provide form 80 and it took almost one year to get the security clearance. whenever I asked my CO about the outcome of form 80, he replied it is not under his hand and he can only proceed further after getting the verification results. Thankfully, we got the clearance after about one year and got our visa as well.
Hope it helps.