Patterns typically have separate instructions for the right and left front pieces and a single instruction for the sleeves. I always knit the two fronts at the same time and then two sleeves at the same time. I use two balls of yarn, cast on the stitches starting with one ball and then switch to the second ball, casting onto the same needle. If the item is large I use a circular needle to accommodate the two pieces. I just alternate from one piece to the other row by row. I know my mother did this as well, so for the longest time I did not know that most Knitters work on each piece separately. I find it saves me a lot of time in tracking rows and keeping track of increase and decrease stitches. Working this way means I rarely have any discrepancies between the two pieces. If I do I'm more likely to notice them quickly.
When working the fronts simultaneously the advantage is that the reverse shaping becomes visually obvious in a way that is not so apparent when working each piece separately. It wasn't until I started teaching that I discovered the reverse shaping instruction was such a problem for many Knitters. It also makes the right side vs. wrong side shaping instructions clearer. I really noticed how much it simplifies things recently while working on fronts with dart shaping. Much more detail was necessary to write the pattern out with stitch counts highlighted than when visual placement was used.
I'm curious, do many others knit this way or do you always knit each piece separately?