It doesn't matter, one row is about 1/6 or 1/7 of an inch and when you're done, that's not noticeable - all patterns do it this way. The armholes will probably have the same number of rows to them, because the first one bound off will also be bound off first at the shoulders.
You can't BO at the end of a row unless it's the very last row; the yarn would be at the edge, with the bound off stitches between it and the rest of the stitches you need to keep working on. Decs can be done at the beg and end of the rows, but not a BO.
sue- knitting heretic