What is the usefulness and value of CERT?

I was asked a question on the topic of what is the value of CERT to professional response.  My initial response was 80, 20.  Professional responders are trained to handle issues from the very trivial to very serious situations, during normal day to day operations they handle 100% of all issues.  But in overwhelming situations, professional responders must prioritize response efforts to where their efforts will do the most good, so professional responders are only able to handle 20% of what occurs in a disaster situation.  The remaining 80% are simple issues that are not critical, but over time can become critical.
Same with damaged homes, small fires, and displaced or lost persons.  During a disaster the 20% of the issues are visible and 80% of the threats to the community are invisible.  That is the value of CERT, emergency services can deploy CERT with its basic training on these simple hazards to keep these small issues from becoming big issues.