I rarely pixel large enough to need pixel line art. I mostly do place the pixels one by one when I do smaller (8-24 px) sprites. Excessive internal lines at that size can be harmful. you need to work more with contrast between color fields to suggest borders.
If I do larger stuff (hundreds of px) or stuff with many colors, I just paint big, scale down and clean up.
I'm not sure, but if I were to do medium sized stuff (24-96 px?) , I'd probably wouldn't do line art. I'd make masses of solid colors, then add clean outlines later. I think pixel line sketches at a medium size would probably be too jittery and noisy. It's difficult to get a feel of the masses if there's too much black and white noise.
