In my "former life" I worked in a knit shop. We discouraged knots. The only time I use them is at the beginning or end of a row. I usually just knit 2-3 stitches holding the tail of the old yarn and the beginning of the new together and leave about 4 inches on each to weave in. Never had a problem with stitches coming undone and it usually doesn't show in your knitting. Course it depends on your pattern, too.

Knots should just be a temporary fix until you can weave them back to the edge and incorporate them into your seam. Knots in knitted items feel lumpy and could possibly come undone with wear. It takes a bit of time to weave them in neatly but you will be much happier with the result.

On fine yarns I knit both tail ends together for 4/5 stitches on thicker yarns always join at start of row. Never had any problems with unravelling!!