Long thread lengths tend to tangle more, it tends to catch something on your work space or on your project, it slows you down pulling over and over thru the beads, and it wears on the thread in many designs causes freaying or weak spots. Recently, I have about decided I should stop telling people how much a project requires if only to protect people from themselves and unnecessary frustration.
I watched one lady struggle in class with 5 yards of thread. I suggested she "park" half on the Spoolie I had provided. She didn't want to do that. Ok I said, suit yourself I thought and I moved on to other students. She continued to struggle. I suggested she cut the thread. "No I'll manage." I continued with other students. During this time, I showed several how I like to add thread. I untangled "Miss Stubborn" a few more times. I suggested cutting again...
Finally after wasting a couple hours she relented and let me cut a lot off. It wasn't 15 minutes before she said "This is much better." At the end she said she should have listened, the shorter thread was a lot better. Ok, we learn a LOT of our lessons the hard way.
I get it, many bead weavers struggle adding thread. Others dread threading needles over and over. (Please try the Tulip needles if you have problems threading needles - they are easier and worth the extra money.) For whatever reason, people often take more thread than is easy to work with. It is actually counter productive. The time lost adding thread is nothing compared to the frustration of tangles, knots, and pulling over and over to use a long piece of thread.
The only exception I make to taking a little over a wingspan is when I can park thread. That can be done many ways. I like the little Spoolies, but a sponge roller works well, as do little embroidery floss holders. You can take twice your comfortable length, find the mid point, and store half the thread on your device of choice winding it from the middle to one end. This technique works similar to a bead stopper with the storage device acting as the bead stop. The thread is then available to use later without weakening the thread, slowing you down pulling over and over or taking out knots. This works well on constructed designs which go back and forth or on a design which works equally well in both directions. It does not work with all designs.
The long and short (pun intended), is that it is a happy day when you figure out that shorter is better for most of us when working with needle and thread.