what it is good for is:
(1) credibility in court
(2) liability reasons
if you ever instruct anyone, and that person uses your training in a deadly force encounter, you bet you will be subpoenaed into court to testify that this person did what you taught them to do.
now, in order to have any credibility in court, and/or to be recognized as an expert witness by the court, you will have to demonstrate that what you taught is correct, besides having the training and experience to be an "expert" in the subject matter (use of force). by being NRA certified you can show that your lesson plans were approved by NRA, and/or you were teaching the "NRA way" how to do it.
that being said, the NRA states that they have never had any court challenge the validity of their firearms training. so, that definitely helps you in court.
also, the NRA offers liability insurance to all of their certified instructors. definitely a plus if you are looking at instructing. the liability is tremendous when being a firearms instructor. if you are out there teaching and don't have the training, experience, certifications, and/or qualifications to teach, you may find yourself exposed to alot of liability that a civil attorney will be more than happy to point out.
my credentials as a NRA instructor are via the NRA Law Enforcement Activities Division (LEAD) which can be seen at this link:
http://www.nrahq.org/law/
my instructor was Mark Fricke who is a retired Prescott, AZ Police Officer. he was a great instructor. he didn't hesitate to jump your sh*t if you didnt do something that was prudent. that made me learn.
if you are thinking about instructing, start building your resume. LFI is a good start, but try to attend as many classes and instructor courses as you can. another thing is experience. training is great, but without any experience you're an academic instructor (all classroom theory and no real world experience).
i find that the best instructors are the ones who have both documented training and experience.
my two cents.