If I want to weave another piece with the same specs as the previous one, I can tie newly-measured yarn onto the old warp. It saves a lot of work, but I need to tie hundreds of knots. Sometimes it doesn’t feel like I’m saving myself much work. I do like the fact that the tying-on process is usually error-free. It is a fairly horrific mess at times, see photo below, but it all smooths out under tension.
I’m tying a dark grey and silver warp onto a black and tan one. I’ll post a much neater photo tomorrow, all parallel warp ends and fancy twill.