Well how about this scenario, It's 1630 and you want to get a late afternoon flight in the still air, you take off,fly around admiring the view when you think geez I better get back, it's getting late. So you make inbound call and you get a 30 mile inbound from Captain Qantas with a straight in approach eta same as you, asks your intentions. I'll do a orbit at 5 miles and re-join when I here your 3 mile final call.
No worries, but then you get inbound calls from twin prop aircraft also wanting straight in approaches calling No 2,3,etc meanwhile your still flying around outside the circuit area freaking out because it's getting dark and you are VFR trained and in a VFR aircraft. This is a normal thing at YPPD 1/2 hour before dark,I know this because I enjoy listening to all the radio traffic at this time on most nights.
If you dont hold your ground the commercial guys will push you back where you may find yourself in a lot of trouble.
3 legs of circuit, once called onto base you have right of way unless aircraft on 1 mile final. No dought the commercial guys will try to bluff you but these are the rules. If you don't sometimes enforce the rule you may find yourself in flying conditions your not trained for. Look at AIP ENR 1.1-83 64.6.4, a,b,c,d, especially (d).