I have a slightly different reason for having more than 1 project on the go at the same time - I often take my knitting to the bar/restaurant that we expats hang out at, and I can only do 'easy' stuff when it's dark & smoky & I'm talking too much
So if I get to a pattern section, or anything I have to keep count of rows or stitches for I just knit that at home in peace & quiet. So right now I have my huge booga bag that I take out each evening & a mitten (yes, mitten singular!) that I work on at home.
But since I'm defnitely a 'starter' rather than a 'finisher' it's probably just as well I only have a Boye set so just 4 cables - having no needles forces me to stick to only a few projects on the go!