My 180SX. 30mm widebody overs in the rear.
275/40/17's on 9J's... +13 offset. Fenders not cut (just pulled/rolled)... Wheel spacers etc not used:
Front: 235/45/17, 9J's... +15 offset. 20mm overs (if anyone was wondering).
So NO- it's not a must.
However, cutting/pinch welding the rear fenders WILL give the option for wider wheels at lower ride heights. On my current USA build, I had the fenders cut/welded up to the body line:
