Years ago, I had the MCL highway pegs. Maybe it was suspension issues along with the way I ride, but I got to the point that I was dragging the bases, on both sides. Basically, the little knuckle that the pegs pivot on were grinding down. More on the right than the left.
On the way back from EOM, I was getting into Nashville when a 3/4 ton Chevy Truck in front of me skimmed a pretty large road 'gator and sent it spinning. I hit that at about 70mph. It slammed the bottom of my bike, and my right foot. I don't remember if my foot was on the highway peg, but I know it was open, and I remember thinking that peg saved my foot from some decent damage. At the next gas stop, the fairing was loose, and I had to pop it back into its grommet.
A few days later, I noticed an oil leak coming from the right side clutch cover. I removed the highway peg mount and the bolts were twisted pretty good. Yamaha fixed the leak, saying the gasket had shrunk, letting oil escape. Maybe it was coincidence, but I'm not sure that leak wasn't caused by the force being placed on them by the pegs. Now, tons of people have used them without problems, so I'm sure the base dragging and the tire 'gator didn't help.
I took the mounts off and sold them, cheap, to some guy here. The right mount plate was bent and I had to buy new bolts because the ones I took out were way to bent to try to use again. I have had no leak issues since taking those pegs off, and I'll never put them on again. I have found I have plenty of movement without going all HD style.
Just MY experience, and mine only!