I am one of the one-at-a-time quilters. The reason is that is all my brain can focus at one thing at a time.
If I was to star two or three quilts at a time I would get so over whelmed I would never get any of the quilts done.
I have trained myself to just work on one quilt or project at a time. If you can do more than one thing at I time I truly admire you, I wish I was a person who could.