Armhole shaping question

Shape armholes: Cast off 6 sts beg next 2 rows. 83 (87-91) sts.**

My understanding of this is that I am to bind off the first 6 stitches of the next row and then knit ALL the way across. Then I am to bind off the first 6 stitches of the next row and purl my way across.

Wouldn’t this screw up the symmetry of the sweater? Shouldn’t I be casting off 6 stitches knitting across and then binding off the last 6 stitches of that row (ie knit row) in order to preserve the symmetry? Is this what I’m supposed to do, and have I just read the instrcutions wrong?

You can’t bind off at the end of a row. Your yarn will be in the wrong place.

Do it at the beginning and finish the row, then do it at the beginning of the next row and finish that row. Those six stitches will be technically ‘off’ by one row, but it won’t make a bit of difference. Every sweater is made this way.