The back loop only is the last round of the base / first row of the side. I turned my work and sc around on the wrong side. It has given the definition I wanted, while still using both loops. I'm happy with the look.
IME ctbl produces a looser stitch which you may or may not like for a given project. Most of the time for bags I prefer a tighter stitch. It all depends on the desired result. If you're following a pattern that instructs you to ctbl only then I'd say go ahead and do it. Otherwise just see what you like better.