As security involves intelligence jobs, there is no info as to how they do it can be released to public. Fingerprints are used to coordinate with other national police agencies or interpol to find out more info on your personal background.
Why?
Because Visa Office does not always trust the paper Police Clearance from your country, there are many fraudulent documents that were tracked down. There are fraud detector machines at Visa Offices, even the documents are real, it is at their discretion to request extensive checks.
CSIS is responsible for this in-depth security check. So for those whose fingerprints are required, be prepared for a bit longer wait because of your background. No matter how long you've been here in Canada if your background triggers their attention or if the PCC documents look suspicious then for sure they will request fingerprints or other types of personal security check.
They cannot be 100% successful, but I believe they will strive for at least 90% success rate to make sure all PRs are security cleared. If you believe you are cleared, please allow them some time to work on your case.
