In canada, unless specifically asked... you only need to read back the ident and squawk code. some airports do things a bit differently and give the pilots more info then they need. Because of that the pilots feel that they need to read back more of the route. In reality it is just a waste of time and the pilot still only ever needs to read back only the squawk code.
The reason you would need to read back more then just the code would be that part of the flight planned routing has changed. This could occur because the pilot filed a non preferred route, the pilot filed the wrong routing altogether, or the pilot just plain screwed up and transposed a VOR or something. YZY instead of YYZ.
At some airports we also have a data link that gives the airplanes their clearances.. So the pilot doesnt even need to read back the squawk code. The pilot gives the controller the discreet 4 digit computer generated code (something like 4A3R) If this matches what the controller has on his screen then thats it. If not then the whole clearance has to be read to the pilot.
Why dont they just use the 4 digit transponder code??? well that would probably be too easy..
haha
Im not sure on that one...