I'm always in favor of less sewing myself. A couple of thoughts:
1: They're probably allowing a stitch on each end for selvedge, so you'll have to account for that if ... there's no selvedge. That's only really an issue if there's a pattern stitch though... a couple of extra stitches size wise, even on a baby sweater probably isn't gonna be a big deal. (I guess if you're using something uber-chunky at 2 sts/in it might be an issue, but what baby sweater is made out of yarn THAT thick? It'd weigh more than the kid!)
2: If there's only one repeat of each color, you can just join the new color in as you come to it. No need to carry it along. Since it's a cardigan, there's no "jog" to worry about in the stripes and the ends from the color changes can be easily enough disposed of.
3: I've yet to actually finish a sweater, so you should take anything I tell you with that disclaimer.