A sweater worked in pieces is easy to take with you, a sleeve is really not much bigger then a sock and its a lot less conspicuous then a big pile of sweater in your lap (and more comfortable in warmer weather)
2. Less to unravel
The argument I always hear for top down sweaters is, you can try it on, but if you knit the back of the sweater first you can audition pretty much everything about the fit of the garment and its only about 1/3 of the work, by the time you’ve knit that one piece you’ll be able to see if it fits, if you like it, if you want to keep knitting it… and its less work then if you knit a top down to the underarm or a bottom up to the waist. You can put the finished back piece onto a piece of clothing you love the fit off and see exactly what (if anything) you’d like to change, before you continue with the rest of the sweater.
3. Easy to tailor
The sweater worked in pieces is easy to change. This is pretty much the premise of Amy Herzog’s Fit to Flatter, if you’re really interested in a lot of fine tuning of your hand knits, you should check out her book, but its really really easy, and all you need to do is create a schematic based on your own measurements and a good swatch and you have all the information you need to make every sweater fit exactly how you want it to.
4. Stronger and longer
A sweater worked in pieces and seamed together is more stable, that means that as the sweater gets worn and washed over and over it will hold its shape better. Yarns have a tendency to break in (like jeans and or shoes) and a little of that is OK but some yarns (super wash wool, cotton, alpaca, silk…) tend to keep breaking in … more… and more over time… I still mourn my most favorite pullover that fit like a glove when I made it, and fit my husband like a glove 2 years later (I’m a 35-36″, he’s a 42-44″).
5. Hand Dyed yarn
Hand dyed yarns all have a little but of pattern to them, even the most solid dyes still have a little variation and we like that, but if you’re making a garment the look of the fabric will be different on the body, the sleeves, and the yoke because the pattern created by the dye is determined by the length of the skein the dyer used and the rate that the knitting takes up yardage. A the number of stitches sleeve round is very different from the body round, hence the yardage is different. But a sleeve row is pretty similar to a sweater front and so the most uniform way to knit a hand dyed sweater is to work it in pieces (alternating skeins is a great idea too, in pieces or in the round…)