It's never *required*, in that it can be assembled with the edge of the turbo hitting the TGV. At some point, folks think that it's likely that this would mess up the TGVs, necessitating the removal/porting.
My thought is... if you dont HAVE to have the extra 5hp, and there is no extra labor involved in waiting until something stops working, why not let the two bump into each other for awhile?
I have never heard of anyone first hand telling me that their TGVs were ruined by the 3" turbo.
I have a 3" green and decided that I would rather have the 5hp (or whatever it is) that porting the TGVs would bring, now rather than later, as well as the fact that I *think* it saved some labor when combined with the injector and turbo inlet swap. With the APS inlet, it sould very well save some labor to do it at the same time.