If you want to sell items that you have hand made, efficiency is essential. Efficiency can come in many forms. It could be finding a new way to do one of the steps along the process or doing a large number of the same item at the same time.
When I decided to set up my loom to make some bookmarks, I went for a four meter warp. I estimated that I could make nine bookmarks with that length. My little loom can't handle much longer than four meters anyway, but it would give me probably 3 more bookmarks than a three meter warp. You have to expect to lose about half a meter from the set up process.
As it turns out, I managed to get eleven bookmarks. I had a timer going the entire time and I checked it regularly. It took me an hour and a half to set up the loom for weaving. By the time I was finished weaving the first bookmark, the timer was at 2h 11m. Just over two hours to weave one bookmark. And that doesn't include agitating it in water, letting it dry and pressing it afterwards. That also meant that it took me about 40 minutes to do the weaving and the edges for one bookmark.
Part way through, I also switched shuttles. I didn't think that one of the ones with the bobbins would fit, but it did! And that saved me another 5 minutes per bookmark.
So it took me 2h 11m to do one bookmark and 7h 35m to do eleven bookmarks, averaging 41 minutes each. Now that's the difference efficiency makes!