I just started climbing and while observing other climbers unhook themselves to transcend limbs I always got this feeling of unease watching them. I decided that I would use 2 flip lines for transcending limbs. My boss said it was a good idea since it is a pretty common situation for falling.
Yeah sure, why not... as the replies above would imply some do, actually alot do...
Unclipping is the dumbest thing you can do up in a tree.. yeah we all free climbed trees when we were kids... but we were exactly that.. Dumb! Regardless, you don't necessarily need two fliplines to keep your points of contact.. What you can do is, (& its a little harder to do with a steel core, especially depending on how stiff the brand is) you can create a completely seperate lanyard out of the tail of the existing one by using a 2 biners & a prusik.. it's just called a 2in1.. There's also the "DEDA", as i think it's called.. Double Ended Double Adjustable.. I can't remember exactly on that one.. To be honest, there really no excuse to have to completely unclip as there are a hundred different ways to maintain points of contact when navigating obstacles. One of the more simple ways is to use your climbing line... & Even If your tied in with it above & you need to maintain your two points of contact, but have the need to unclip your Lanyard, you can just use the tail of your climbing line..
So they're realy is a ton of ways to go about keeping it safe.. I actually just spliced a short lanyard up to see how running two would work out.
I think running a double ended system /2in1, whatever its called, on a longer climb rite steel core might not be too bad. I felt one out recently & was amazed at how flexible it was while still maintaining the ease of flipping. It also looked allot thicker than the 1/2in rope logic i have. It had to have been a 9/16 or something, so you would think heavier & stiffer, but it flexed way better than my 1/2in.
Anyhow.. there's lots of info here on this subject.. you deff won't have a hard time finding it
Good luck & be safe my friend!
EDIT - The Steel Core i liked the flexibility of was not a Climb Right. It was made by U.S. Rigging Supply, which is even odder as i had always been under the impression those were exceptionally stiff.