Multiple WIPS

How many works in progress do you normally have? Do you think it's inefficient to work on a few things at the same time, especially if they're the type of pieces that will take awhile? I'm working on one "larger" painting (11" by 14") but then keep messing around with some smaller ones — not to mention that I'm also trying to learn how to work with colored pencils.

I kind of jump from one to another without accomplishing much, sometimes, especially when there's a hard spot I'm having trouble fixing. For my larger painting, I need to finish some of the background (which is pretty simple) and then paint the horse's main and fix coloration... It takes a while for me to get something looking decent so I get impatient waiting for layers to dry and want to do something else and start another.

How do you avoid jumping around so much and just focus on the same painting? Also, do you think that having multiple works in progress is beneficial or is it just inefficient?