I tend to make a bunch of tops and then quilt a bunch in a row. I was thinking about this question just yesterday as I was thinking about how I have several projects going on at once. The thought of only one project completely stops my creativity as soon as it gets a bit on the tedious side. If I have several going on at once, and don't feel like doing something boring at the moment, I can work on the other project. Plus, I tend to prefer to do a lot of pressing/ironing at once and so I prefer to have a lot to iron to make turning on the iron worth it.
For example, I had some 9 patches done and needed to lay them out on the ping pong table to get the colors in an okay position (I had previously sewn them). I have a QAYG project ready to layer and quilt (but I needed batting--finally bought batting a few days ago, so started on that--am now on the hand sewing part of that), had my embroidery machine going and was working on a disappearing 4 patch (I'm finding it not very interesting, so having a hard time pushing myself, but managed to make myself do a few blocks.)
I find that if something isn't really interesting, i can usually MAKE myself do a few blocks or a few seams before going on to something more fun. If I KEEP doing that day after day, eventually I will finish that project that wasn't as fun to do as I thought it was going to be. So, the idea of doing only one project at a time, is, to me, rather awful. It is areal "creativity stifler".
But I currently have about 60 quilt tops to quilt--all pressed and ready to go. I just bought two 50 meter rolls of batting, however, so I'm planning on getting to work on them. (Many of these are charity quilt tops and will be tied--some I will continue to practice my FMQ on and some are personal and will be quilted by machine.)