If your machine has a stretch stitch, you can use it for seaming, and some experienced knitters do.
But it's likely to give you bulky, obvious seams (especially on the sleeves) and a factory-made look, while doing the seams by hand gives you far more control over their tension, a less visible seam and a better drape.
Don't take anyone's word for it, though.
Try machine stitching a swatch. Pin or baste carefully first, use the stretch stitch and loose tension and see how you like the results. If you don't like the look or feel of the machine stitched seam, hand stitching is the way to go, and once you get the hang of it, I think it's just as easy and almost as fast.