The notices in newspapers for when a business first opens are particularly useful. Other notices for when a business was bought and sold are also relevant; I've been able to use them to track relationships between possible family members.
The ads placed in newspapers are fairly easy for Newspapers.com to pick up, because ads back then were so text-heavy, and often contained the name of the business owner.
Two other sources for searchable older newspapers are Fultonhistory.com and the US Library of Congress' Historical American Newspapers.
One thing I have found - smaller newspapers back then would print news of relatively small events that took place even several counties away. For instance, I found the notice of my grandparents' marriage license, taken out in Hagerstown Maryland in 1913, in the Harrisburg, PA newspaper.
Lak/Lok/Liak/Lock and Kalon/Kolon in Zagare/Joniskis/Gruzdziai, Lithuania
Lak/Lok/Liak/Lock in Plunge/Telsiai in Lithuania
Trisinsky/Trushinsky/Sturisky and Leybman in Dotnuva, Lithuania
Olitsky in Alytus, Suwalki, Poland/Lithuania
Gutman/Goodman in Czestochowa, Poland
Lavine/Lev/Lew in Trenton, New Jersey and Lida/Vilna gub., Belarus