I have an Oxaback Lilla and a Glimakra Standard, which I have been able to successfully warp. My process has been pretty straight forward:
1) Beam on warp
2) Hang shafts from countermarche jacks
3) Thread, sley, tie-on and tension warp
4) Connect upper lamms to shafts, and lower lamms to jacks if not already connected
5) Put locking pin in place, and tie up treadles
6) Remove locking pin, test tie-up.
7) Insert locking pin and make any necessary changes.
That's been my routine, which has worked prett well. There's always some fiddling with the tie-up to get a good shed, but I just assumed that was part of the process. Anyhow, I was having some difficulty getting clean sheds with a new tie-up (8 shafts, 10 treadles), and was re-reading Joanne Hall's book on the subject, when I noticed something that I obviously missed during my original pass through it. She says to start with the shafts on shaft holders, AND to put the shafts back on shaft holders during any tie-up activities. That floored me. I have only used the shaft holders to get the shafts out of the way while beaming on, if I haven't bothered to remnove them completely.
I have great respect for Joanne's knowledge, so assume there is a good reason to put the shaft holders on for those times that I use the locking pin ... but for the life of me, I can't figure out why. The shafts are attached to the jacks, which are held in place by the locking pin, so what does the shaft holder do, other than spread them apart, front to back? And if that is the reason for using them, what advantage does that offer? I would be grateful for any insights on this.
I believe what you & I are calling locking pin do the same job as what others call shaft holders. I have locking pins but have used shaft holders on other looms.
It can be faster and easier to put the shaft holders on than to put the locking pins in. Especially on the much older looms where the locking pins are in the center of the loom. On a wide loom, it can be a reach to get those pins in. And on some Louet looms, it can take a while to put the pins in, as the pin needs to go through holes in the Texsolv cord and the cords do not stay lined up. And on some Finnish looms, you have to move a wooden cover out of the way to get the pins in. So, for a small change in the length of some treadle cords, it can be easier to simply put the shaft holders on to hold the shafts stable while you make the treadle cord adjustment.
The shaft holders can also make it faster and more secure to put shafts on for the first time, before the length of the tie-up cords has been set.
And, some looms may not be as easy to warp as your particular countermarch loom. For some, it may be more comfortable to thread the heddles in a different position than under the countermarch. On some looms, the countermarch does not easily move, or cannot be moved. In that case, if there is a full sized castle, one can hang shafts in a different position, from a pole, on the shaft holders and then after they are threaded, hang the shafts uner the countermarch. There are many different countermarch looms.
Plus, you are now an experienced weaver. You are successful at warping and you could probably make changes in your methods, based on what you are warping and still be successful. I once got a call from a man who simply said "Help, I just dropped all my shafts on the floor and the heddles fell off." So, I thought that a little extra precaution in the instructions would be good insurance for some beginners.
shaft holders (I call it a shaft craddle)
I use the holders on every warp. I do this because I move the harness to the back of the loom by the warp roller and sit inside the frame on my bench to thread heddles. Once threaded, I move the harness under the countermarche, I tie on the warp to the cloth stick and adjust the harness height with the holders to centre the warp in the reed, then tie everything up. I put the locking pin in place through the jacks before I do anything at the loom at all. It is like a super sized 3/16" needle with a handle on the end. :)