The simple thing to do is: find out before you set off.
A considerable number of airfields/airports do not permit overhead joins and expect you to join (as already stated) to join either straight in or downwind/base leg. If you were to try and join overhead at my based airport, the chances are, you'd meet something large, fast and bristling with pop guns, going the other way. Each airport has it's own reasons.
Joining overhead is a time consuming procedure which also restricts the climb rate of departing aircraft, and I.M.H.O, I would encourage any pilot to be prepared to join in as direct a manner as possible, as dirested by ATC or the airfield operator.