Is a weather briefing required?
Yes, at least for flights that are not in the &quot;vicinity&quot; of the airport.
FAA CFR 91.103

Each pilot in command shall, before beginning a flight, become familiar with all available information concerning that flight. This information must include--
(a) For a flight under IFR or a flight not in the vicinity of an airport, weather reports and forecasts, fuel requirements, alternatives available if the planned flight cannot be completed, and any known traffic delays of which the pilot in command has been advised by ATC;

You are not required to call Flight Services for a weather brief, but you are required to get the weather reports (which can be called a personal brief). If you do all flight services and happen to have an accident, then your accident will contain the details about your call.