I got to play gas pipe installer at my house. Your choices for bends are pretty limited to 90 and 45. Besides being not so versatile, every bend has to have a place for a potential leak. When I got done I looked at the run and thought how much easier it would have been if I could have just bent the pipe. I have a Chicago bender that would have made it possible to do the entire run in one or two pieces of pipe.
A good pipe runner won't gain a thing by using factory bends.
I had to run a rack of 2" EMT behind all the other trades. I think there were six 2 inch and 4 3/4 inch that had to offset perfectly to get through all the other stuff hanging from the ceiling and hit the wall where it had to. The offsets had to have 40 degree bends. Not much room for error, either, and being 18 feet off the ground didn't help much.....
I had a ratty old 555 for the big stuff and a hand bender for the small stuff. I used a magnetic inclinometer to get the angles perfect. The small stuff could be wrestled, but I still checked everything on the floor before it went up.
I was alone for that run, my partner was in Vegas, so making a boo-boo would have been even worse.
No way could the run have been done with factory bends unless the other trades moved their stuff, which wasn't going to happen. If I hadn't been taught to bend pipe, I would have been screwed. All the other stuff required 2 people.