Why use pre-wound bobbins?
 

This is something I've puzzled over from time to time. What is the upside of using pre-wound bobbins? It only takes 60 to 90 seconds to wind a bobbin, so I don't see how saving time would be an issue. Is there a benefit I'm not thinking of?

I wind my own bobbins, but I have longarmer friends who like the pre-wounds. It can be hard to find a good stand-alone bobbin winder if one didn't come with your machine. Also, if you want to use the same thread in the bobbin and on top then you have to choose between buying two of the same color, winding a bunch of bobbins ahead of time, or moving the cone of thread from your longarm to your bobbin winder and back again. I've been told that the pre-wounds also hold more thread, though I don't know that for sure.

they do hold more thread and are wound more evenly and tightly that home-grown bobbins.
i find fewer tension issues when i use pre-wound.
a cost comparison depends on which brand of thread you use most often. sometimes the pre-wound bobbins cost about the same - maybe less - than conventional.

but it really is a matter of personal preference.

I use prewounds because I know they are wound with the correct tension.

I have used pre wounds for years. Glide magna and Superior are my choice now. The bobbin thread is wound tight and full. They last a long time while sewing. I rarely have bobbin thread issues. To me buying pre wounds is the same as buying thread when I need it,

We tried many options but could not wind a decent bobbin for my friend's long arm. As soon as we went to pre-wound, most of our problems ended and as Partrice said, the bobbin held much more thread.

Back when I first started using an embroidery machine, I thought pre-wounds were great. I bought a box of NEB pre-wounds. Had 144 filled bobbins in it. That was back in maybe 2004. I still have a few bobbins left but now as my new machine uses larger bobbins, these pre-wound bobbins just rattle so I wind them onto the machine's bobbins. They don't fill it completely but there's a lot of thread on those pre-wounds. All my machine's have a bobbin winder on them and they all work fine so rather use them instead of buying pre-wounds that cost much more than me just winding my own. I ordered bobbin thread in various colors from BFC back when they were selling threads so I have quite a bit to last me a very long time.

I'm too frugal to order pre-wounds. When I run out of bobbin thread, I usually wind 3 at a time. Even that does not take long.

Magna Glide pre wound bobbin size L has 130 yards of 60 wt. thread. Size M has 230 yards.
Super Bobs cotton size 15 and L has 70 yards.
Size 15 and L in Superior poly holds 134 yards.
Superior M style poly has 230 yards.

I use pre wound Magna Glides on my Juki TL 2010 which is on my Cutie frame. They give me more thread per bobbin so I stitch longer before changing the bobbin. Even winding so my tension is consistent. Easier to install thread into bobbin casing and casing into machine, they have a magnet that goes into casing and is held there no more fumbling as I insert into machine. For my other machines I wind myself.