When a family historian is looking at ancestral documents it is important to give consideration to the other names one finds in the document. Friends, Business Associates, Witnesses - conducting at least minimal research on these individuals is advisable. Not doing so may lead to missing out on some major discoveries.
Examples from my own research:
(Links are to past entries where I discuss these instances in greater detail)
1) Max Wieselman - Selig Feinstein's business partner
2) Michael Flynn, County Clerk for Clifford Cruvant's name correction
3) Marcus Hast, cantor at the marriage of Sol Newmark and Sarah Nathan
4) Bessie and Iva, friends of Mabel Fulkerson, and fellow heroines