Well, bolt-on installation is for the person w/ few tools. I installed my first set in the driveway, by myself, with a 12V cordless drill, 5/16" bit and a 9/16" socket in my ratchet. Took me two days, sice I needed to charge the drill battery pack overnight after doing one slider. If you have (or have access to) a welder, then welding is somewhat quicker. Usually takes me ~1 hour to weld on sliders and 90 minutes to bolt a set on, depending on how many mounting brackets.
- http://www.4crawler.com/4x4/ForSale/Docs/NerfBar_HowTo.shtml

Bolt-on = bolt-off, and I have had mine off a few times over the years. First time was when I changed from 1" to 3" body lift. Removed and sold the original Americal Metal sliders I bought then made my own fit to the 3" lift. Then those new sliders have been off and on a few times, once to make a jig from them, another time to sand and repaint them (probably be doing that again this year) and one or two times working on the truck. For example when installing new spring hangers up front, was so much easier with the sliders off the frame. Sure, all the above could bhave been donw with the sliders on the truck, just would be more difficult. And sure, welded-on sliders can be cut off, I have done that before and that is a PITA.

I've had both round and square tube sliders and I now have square tube:
- http://www.4crawler.com/4x4/ForSale/RockSliderZ.shtml#Background

Sure, round is stronger/lighter and for a roll cage, round is the only way to go. But for something like sliders, which serve as more than just protection, square tube provides some other advantages.

And of course, you can weld on brackets to the frame and bolt the sliders to those. And there are the clamp-on type mounts where you fabricate each bracket to clamp around the frame and then bolt the clamps tight. In order to get a good fit with those, you need to custom fit each bracket to the frame and you are also somewhat limited in where brackets can be placed since you need all 4 sides of the frame rail clear.

On the other hand, if you have round tube front and rear bumpers, then a set of square tube sliders would look out of place. My front and rear bumpers are square or rect. tubing, so square sliders fit right in.