For many applicants, a fingerprint request has minimal impact on processing, a little delay while the applicant responds to (provides) the fingerprints, and beyond that processing is routine.
Fingerprint requests may be triggered by many of the things alluded to, including simply to distinguish similarly named persons (such as where DoB or other identifying information is coincidental), and including random (quality control) requests.
Any concern IRCC has about verifying the applicant's identity could lead to a fingerprint request. Which is to say, perhaps the main reason for a fingerprint request is simply so that IRCC can definitively confirm the identity of the applicant. Assuming the fingerprints accomplish this, and they should, no problem, back to an essentially routine process.
While I would not phrase things in the same manner as Richard11, the gist of that response may also be true for some, just some, that is for this or that or whatever reason, IRCC may request fingerprints for the record, so to say, to have a definitive identity record. But many if not most of us never submitted fingerprints to CIC or IRCC, and did not need to do so in the citizenship application process either.
A criminal charge related FOSS or RCMP record hit is the likely trigger for a fingerprint request for some applicants, but either the applicant should already be aware of this (having had the law enforcement or court contact involved) OR this too could be about a similar name and done to distinguish the applicant from someone with a similar name and criminal record. Or this can happen if the applicant had some sort of charge which is dismissed or dropped or is otherwise one so minor as to not require a declaration of it in the prohibitions part of the application, but still shows up as a hit in the RCMP name-records query (and thus in FOSS as well). Similarly, U.S. charges can trigger a hit, and again even if the charge is so minor that the applicant did not need to disclose it.
Obviously, CSIS could respond with a fingerprint request, to the referral for the Security Clearance, which IRCC would then make to the individual applicant. If there is a security reason for the request, obviously this is one of the circumstances which could lead to a longer delay in processing.
BUT mostly, for most applicants who are asked to submit fingerprints, it is just a small bump (short delay) in the process and NOTHING to worry about.
