/u/evidentlycat gives a great explanation of the difference between /sbin, /bin, /usr/sbin, and /usr/bin on /r/BSD.

http://b.thumbs.redditmedia.com/ogsjP2Dly5R9Y796Qg92fW4pI9kRJY-DIiBAISX4ebk.png

I use the terms “dynamically linked” and “statically linked”. A statically linked executable is independent: it does not load a separate C library, instead, the executable itself contains copies of code it uses from the C library, and interfaces with the kernel entirely by itself through syscalls. A dynamically linked executable loads an external library from a file and calls functions in it.

bin is for binaries which are useful for users without elevated privileges. /bin contains statically-linked binaries which are “fundamental to both single and multi-user environments” according to hier(7). They may be used in the tiny installer ramdisk. Most things in /usr/bin are dynamically linked and all of them are inaccessible in the installer.

sbin is for superuser binaries and daemons, i.e. things not useful to users without elevated privileges. Everything in /sbin is statically linked and accessible in the installer. Most things in /usr/sbin are dynamically linked and all of them are inaccessible in the installer….

Original post from /u/evidentlycat: http://www.reddit.com/r/BSD/comments/2szofc/eli5_why_is_separating_binaries_into_bin_sbin/cnudxzs

Official documentation on filesystem layout: https://www.freebsd.org/cgi/man.cgi?hier%287%29