The KFB is one of the easy methods for adding a stitch to your knitting, so it’s well suited to the beginning knitter. It’s essentially just a stitch you already know, with one extra step. In fact, the only increase I think is easier is the yarn over.
The main disadvantage of the KFB is that it’s a pretty visible increase. When you knit into the back of the loop of the old stitch to make a new stitch, it creates what looks like a purl bump across that new stitch you’re creating. If you’re working stockinette stitch or some other stitch patterns, that can lead to visible bumps across the right side of the fabric.
if you plan carefully, you can make these little bumps part of your design, like I did with the bottom of my Emily’s Garden Tea Cozy (pictured in this post).
Yes. KFB leans to the left because it creates a new stitch on the left side of an existing stitch.
KFB is worked by knitting into the front and back of a stitch, while PFB is worked by purling into the front and back of a stitch. Although the two stitches use the same parts of the existing stitch, the yarn is wrapped differently to create either knit stitches (in KFB) or purl stitches (in PFB).