For me it is simply all about being happy with my final print.
I try to capture on film what I think will make a good image. If I am successful, and if the subject fits the format I am using, then it is likely to end up being printed full frame (but mostly without the edge of the rebate). But if the strongest image can only be isolated by cropping, then that is what I will do.
I understand the benefits and pleasure that can flow from imposing limits on oneself (eg only using one lens, or only shooting in B&W, or always printing full-frame, etc), but to insist that such limitations necessarily amount to a purer or more rigorous way of working seems a little masturbatory.
Full frame printing can be very satisfying but, if done religiously, some prints will never be as powerful as they could be. That is inevitable.
Ian