When sewing bulky sweater knits, you don’t want the seam to be bulky.

* Sew the seam with the sewing machine.
* Overlock each seam allowance separately.
* Steam the seam open.
* Tack the seam allowances down with a catch stitch.

Source: http://www.craftingfashion.com/search/label/serger%20techniques

A video about this subject: https://www.youtube.com/watch?time_continue=41&v=d783OdG_7fs