It's ok joining on the 45 if know exactly where the airfield is. But, I find that if I'm trying to find a small airfield I haven't visited before it's easier from 2000ft agl rather than circuit height 1000ft. From the overhead it's easier to spot the wind-sock, signal square and observe traffic in the circuit and generally get myself orientated to the field. To use the 45 degree method you have to know the runway in use to plan your circuit which probably implies being given instructions by ATC. "Horses for courses".