All MATZ have an ATZ embedded either 2nm or 2.5nm radius; as a MATZ is 3nm or 5nm radius, you don't HAVE to call to transit, but you MUST call to penetrate the ATZ, hence it's a good idea to call anyway.
A MATZ only exists when the aerodrome it surrounds is operational ie when ATC are in attendance, so at weekends when there is no reply from ATC, the MATZ is not active but there may be flying in progress by gliders or light aircraft including Tutors; this is especially true at Benson and Boscombe Down where they operate 'tower only' ie no radar; they don't listen out on the radar frequency so although you don't get a reply, the airfield may well be active; best to call on the tower frequency at these times (if you know what it is!) if you're transitting close to the ATZ or across final approach.