What's the difference between a Knit and a Knit through the Back Loop?

To me, one of the greatest things about knitting is the subtle variations you create through simply changing the approach to a stitch.  We can see this when we look at a regular Knit Stitch and a Knit Through the Back Loop (KTBL).

Here are images of a knit stitch (bottom) and a ktbl (top):

As you can see the knit stitch (where the arrow marked "A") forms a nice neat horseshoe shape (or an upside down U).  The Ktbl (where tje arrow marked "B") actually has right leg oof the stitch crossing in front of the left leg giving it a twisted appearance.  Utilizing a Ktbl can provide some visual contrast to your work while also creating a slightly denser fabric.  It's a simple easy way to change things up without having to step too far outside of the box.