Sound genealogy research advice suggests that we research names that appear as witnesses on documents our ancestor signed. That’s good advice. Those names could be clues.
The key word is could. Like much advice it all depends on context and the specific situation.
The more often the same person appears as a witness on documents my ancestor signed, the more likely there is to be a connection between the witness and the ancestor. If the ancestor was an immigrant who did not know the language and the witness name appears to be from the same ethnic group that is suggestive of a connection. In some cases where an ancestor could not read, I have wondered if the witness was a trusted associate of the ancestor who was literate in the language in which the document was written.
But there is always the possibility that the witness was just another warm body who was of legal age when your ancestor went to the lawyer, justice of the peace, notary, etc. to have a document witnessed or drawn up.