I’ll admit it. Voter’s registrations are one of those records that I don’t use too often–not nearly as often as I should.
Having looked at some late 19th century ones online recently for Chicago, Illinois; California; and New Mexico, some things stood out. They can provide the age of the registrant, their nativity (probably only as specific as the country or state), whether native born or naturalized (possibly providing the court where the naturalization occurred), and perhaps the time they have lived in the district where they are registered to vote.
All of these things can be helpful clues–especially for that time period where the essentially non-extant 1890 census is a problem and the person of interest was an immigrant.
These are typically county-level records in the United States.