Learning to "read" my knitting. It helps in any situation, using any technique, any kind of stitch pattern, monitoring your work for and correcting errors, etc. It affects everything I do. Very basic skill but totally necessary.
Yes, this is very important, and for me combined knitting took it to a new level. With combined knitting you have stitches mounted both ways, both with the leading leg in front of the needle and with the leading leg behind the needle. Depending on the orientation I knit the stitches differently. This means I need to read my knitting as I go or I will end up with twisted stitches.