I've made 3 knitted suits. Well, 3 cardigans with skirts-to-match because I had enough yarn leftover! The simple skirt pattern said knit the front and back to match, then seam the sides.
Hmmm. I am a follower...therefore, that's what I did. The skirt turned out very nice!
But, the 2nd and 3rd time I needed a skirt to complement a cardigan...I knit that pattern in the round
...same pattern...just eliminating 4 stitches to the grand cast-on. They turned out just as nice.
My 3 skirts were all bulky yarn, BTW. A sturdy tweed, a Manos del Uruguay and a Rowan Polar.
But, I read someone's comment over at Ravelry, in a discussion regarding the subject of seaming: To Seam, or Not-To-Seam...quite a hot topic.
Anyhoo, one of the more accomplished knitters said that seams help stabilize the garment for a better fit. She elaborated more, but that is the jist of it.
Well, my skirts couldn't care less, they're just tubes wrapped around my hips and legs, & elastic waistbands to boot.....but, I would never take a short-cut for a cardigan or pullover if the designer didn't recommend knitting the fronts and back all-in-one-piece (this eliminates the side seams).
There was quite a crowd of Central Park Hoodie knitters over at Ravelry who were skipping body side seams...to avoid side seaming
...but that complicates the sleeve insertion even more. Then some were also knitting the sleeves in-the-round, too! Can you visualize this: seaming a sleeve "tube" into an arm "hole"...becuase you do have a "hole" after you seam the shoulders! Gads. Well, maybe they figured out how to pick up stitches around the arm "hole" and knit in-the-round down to the cuff!
My head hurts.
I think your sleeveless tank top is like my skirt, except for a different section of the body! Being a follower, I would probably do what the pattern says the first time around, for the experience.