Nerfs are typically cosmetic by design and while can handle light abuse will fail much sooner than sliders.

Unless custom fabricated, most nerfs are built using .120" thick (aka ".120 wall") steel tubing which is fine for most "light" hits but not strong enough for harder hits taken when rock crawling or going over more difficult terrain.

Sliders are purpose build with long term abuse and survivability in mind. In most cases, I recommend a minimum of 220 wall steel tubing to minimize the number of frame attachments (2 or 3) and while still survive repeated hits off road.