Yes,gate preparation helps you for ies also but major point is syllabus covered in gate is much smaller than ies to be able to co-op with other aspirants who are only preparing for ies! Since ies has easier question compared to gate but calculation you have to do on your own,gate aspirant generally start calculating 2*2 using virtual calculator,basically point is a overdependence on calculator is commonly seen in gate student and when u go for ies brain goes blank in exam!
Pros of gate student if question comes from gate syllabus he can definitely solve it.
I am telling about ece.gate vs prelims only!
GATE and IES both these exams are different and tough. GATE helps to get into higher studies whereas IES is conducted for recruiting candidates for engineering services.
Well to answer your question if you are studing GATE 70% of your workm is done for IES exam.
GATE exam requires more critical thinking than IES exams . IES questions mostly involve a linear apporach to solve. But GATE exam questions involve multiple concepts that too applied in correct order.