Once interviews are completed, most employers will seek input from all parties who have encountered candidates during the interview process.
Keep in mind that even seemingly lower level employees like administrative assistants who greeted you and set up your interview day may be asked for their impressions. Treat everyone respectfully and be your best professional self at all times, including informal lunches or dinners with prospective colleagues.
Of course, it is hard to anticipate what each employer will be looking for as they make final decisions about candidates, but it is useful to consider some common factors.