It's not really the lift in the trucks, but the tires that go with the lift. I'm sure others want the heavy duty look of the truss, even though the truck may never see dirt...
The extra large tires provide additional leverage to transmite the impact of a hit. Never mind the unsprung weight and loading on the tube hanging off on each end.
If your running off road with or with out a lift, a truss can be cheap insurance. If a hit is hard enough, the knuckles or spindles will see the hit and the truss is supposed to save the tube, welds and joints that are between the truss mounting points.
I've never seen a knuckle where the ball joint is in brake off. . but I have seen the welds and tube break loose from the pumpkin.
I guess the point being , you can get home with a bent spindle, but your not getting home with a broken axle housing.
On one of my gasser with a lift and larger tires. .
I've bent and axle without a truss. But if I had better shock setup, it may not have happened either. After "bending" the tube straight again and replacing the seals, I put a truss on and a set of dual gas shocks and a better travel stop. From that point on I always leaked a tad bit of 90w from the front seals. . but it never amounted to much.
I should have known it was going to happen since I had felt the front end bottoming out and hitting the stops once it a while from hard off roading. . not a good sign, should have done something. . than it happened , bent the tube on a hard hit.
If you dont run off road hard, dont ever feel the suspension bottoming out,, your probably ok. If you stiffen the suspension to help control the bottoming out, get a truss too.
If you run larger tires, lift... and use it... you've increased the loading on the front tube, during use of the suspension. . and should put a truss on too.
just my $. 02 from breaking and fixing trucks over the last 20 years. .