There isn't much logic to it. The theory is that /sbin *should* be for systems binaries needed to boot the machine and configure basic services while /usr/sbin is for systems binaries that have a more optional or less system-critical nature. But both sbins are on roots path generally, and generally not on user's path.
Don't worry about where it is - just run what you need to. Only worry about where it is if it says 'not found'.