There's nothing magical about /sbin . It's just a place to put things that are typically only used by root. Since /sbin, /usr/sbin
, and /usr/local/sbin
aren't in a mortal user's $PATH, joeuser won't get anything when he types fdisk, but if janeuser has /sbin there, she will.
Of course there's nothing stopping anyone from using the full path, eg /sbin/shutdown . But if you're not root, (and you don't have root equivalency via other means), you won't have the priveleges needed to do anything dangerous.
There's a strong correlation between /sbin and man8, for obvious reasons if you know your man sections.
/sbin is also unique, relative to /usr/sbin and /usr/local/sbin, in that is probably on the root partition. So if for some reason that was the only partition you could mount, you can still use anything in /sbin, even if smoke is coming out of /usr's raid tower. Thus, the things in /sbin are often things that can really save your butt with a near-catatonic machine. Think lilo, fdisk, fsck. Bells and whistles and high-level services are usually under /usr and /usr/local. Of course, there are times when /usr isn't available for other reasons - during boot, or scheduled unmounting. If you need it when you don't have /usr, it should be in /bin or /sbin .
Of course, not everything there is for such dire situations. Many troubleshooting and diagnosis tools live there, especially if it's something that the typical user might not understand or need, but are of interest for the curious (think arp and traceroute, for example). These programs might present limited functionality for non-root users, or perhaps operate in a read-only state.
Of course, this is all just how some people choose to do it. Each system has its own quirks, usually a reflection of the sysadmins's upbringing, tastes, and exposure. Suit yourselves.