I'm young (well, 37) and can remember when having a Police Call on the shelf was mandatory for any serious scanner listener. This was back in the day when if you wanted info that wasn't listed in police call (like businesses), you could either search for it yourself, or pay for data.
I recall going in with a few folks to get microfiche copies of FCC records from my area, going to the library to view the fiche, and then going to the courthouse to look up addresses and names to see what businesses people owned (as some licenses were listed under the name of the licensee, rather than the business name). Information gathering in those days was much harder.
While I confess I haven't purchased a copy of Police Call in several years, it was an institution. I certainly appreciate the contribution Gene Huges made to the hobby.
Also, while RadioReference.com is a fantastic resource, it isn't the end-all, be all. There are many areas of the country where it simply has no real useful data. I'm doing my part to contribute what I can for my area, but on numerous occasions I've gone looking for info that simply isn't there. This will improve with time, of course, but it's not there yet.
I still rely heavily on printed frequency books from trusted sources. I'm fortunate enough to live in California (well, fortunate in this one respect, unfortunate in countless others) where Bob Kelty has been providing highly detailed books for several decades.