If you don't sawzall, you are not gaining extra clearance (for larger diameter tires), only width coverage. Of course when you sawzall, you can't go back! Sometimes the structural lip is removed when you sawzall for fitting Bushwackers, making for more flexible fenders.
Some Bushwacker fenders get discontinued (as in my sliding door version), so if I had to do it again I would buy an extra set and put them in storage.
I know a Hot Rodder who opens up steel fenders for bigger tires. Ultimate coolness. Large expense.
But oh so cool.
New lip tacked in..
And when done, the untrained eye might not even notice... 34's no rub.
Its all about tires not rubbing with your final result. If they rub, its not right.