There seem to be two basic approaches to heel stitch. Most patterns tell you to *slip 1, knit 1* to end on right-side rows, then slip 1, purl to end on wrong-side rows. We'll call this Approach A. Other patterns, however, will tell you to slip 1, knit to end on right-side rows, then *slip 1, purl 1* to end on wrong-side rows. We'll call this Approach B. There are many people who swear up and down that Approach B is much faster than Approach A.
Being someone who likes to try different approaches, I gave it a shot. I found Approach B much slower than Approach A. Why? The unknit yarn kept getting in the way when I would go to slip on the wrong side. Moving it out of the way slowed me down. I knit continental, however, so I don't believe this is a problem if you knit American style. This leads me to believe that one's knitting style determines which is more efficient. Continental-style knitters will be able to go faster with Approach A, whereas American-style knitters will be able to go faster with Approach B.