Gotcha! I follow your meaning, about the boredom issue. It would definitely be complicated and complex to work the FRONTS and BACK as one piece. Each row would have so much to remember.
Knitting in one wide piece (BACK and FRONTS) would be boring to me. "Neverending Rows" so to speak.
I found it to be more interesting to knit the pieces separately.
I start with the BACK, making good notes about what started where, and then duplicating that for the LEFT FRONT, also making good notes about what starts where, then duplicating that but reversing shaping for the RIGHT FRONT.
Some knitting 'experts' commented that seams do add stability and structure. I dunno. Can't add my 2 cents to that cuz I've only ever knit something in one wide piece up to the armholes when the pattern dictated to do so. That is usually with designs that are very complex and side seaming would disturb the pattern. I've made just a few of those types, usually for little girls, but once for my DD. Here is the type of sweater I'm talking about. I made these for my DGS's:
You definitely CANNOT have side seams on these little SPRINGTIME cotton coats!
You are right about the Fair Isle! Who IN THE WORLD would say to knit Fair Isle FLAT?
I can't even imagine the process! Nightmarish.
I heard that the 'not seamed' CPH hung more sacklike on the body. But I can't imagine it looked bad, afterall, it is just a jacket! Who cares? I made a size 46 but with larger needles to get a size 47 cuz I wanted it to be a JACKET not a cardigan. I wear a pullover sweater under it when we walk down to the movies in cold weather. Toasty!
I wear this (Silky Wool):
...with this (Debbie Bliss Luxury Donegal Tweed):
and it isn't tight! It zips up real nice with room to spare!
I think you'll do fine whichever way you put your CPH together...all in one piece up to the armholes, or separates.
However, I do recommend that you knit the sleeves FLAT, seam them, then insert them into the armholes using mattress stitch and those baby clippies I recommend for holding the sleeve into place, with all the edges eases together for a smooth even 'join'.
This is my CPH, undergoing the seaming!
This is my bed jacket, with the sleeves ready to be seamed into the armholes, the flat method, with sleeve and side seams worked after that.