haha your experience may vary. But on my truck, running 0.75" of front lift on Factory 3.0s, 37" KO2s, +12 offset 9" rims, slot delete that pushes wheels out, I still have my fenders.
Also, for me the pinch weld mod is for when the tires are turned, whereas the trimming on the top inside of the fender flare is for full squish. I did the fender flare trimming with a flap disc on a disc grinder, and also dremmel, while the flares were on the truck. I got a nice angle that way (more clearance where you need), and only trimmed what was going to look alright and make a difference given where the fender liner was at.