I'm all about Minimum Input, Maximum Output.
For this towel warp, I was using up a limited quantity of yarn for weft. Since I didn't know how far it would go, rather than design a towel with specific hems and/or border design, I decided to just weave yardage and cut it up to towel length when I was done weaving.
With no obvious cut line, here is what I do.
I measure out the length I want for the towel (including allowance for hems).
At the appropriate length I make a small cut in the cloth:
Then I pull a thread out of the cloth:
This makes a visible line which I use to cut across the width of the cloth:
And then I serge and voila, ready for wet finishing (after I've fixed a few loops in the weft).
Surprisingly the yarn yielded more fabric than I expected. I've still got 4 ounces of the hand dyed 2/20 cotton left! Back into the stash it goes...