Back in the olden days, there were any number of ways to shutdown a UNIX server - even some shortcuts (on a DEC terminal connected to a DG AViiON - if you pressed and released SHIFT six times in rapid succession - you could induce a kernel panic and reboot - handy to know at 3 in the morning after waiting 2 hours fruitlessly for remote support to shutdown a server!).
On Solaris, there was “shutdown -r now” (or -h to halt) - but there were also shortcuts using “uadmin” - e.g. “uadmin 2 0” would sync filesystems and drop the host back to the boot PROM (OK prompt)
And there was various things like “telinit 6” to reboot… “init 6 0”… etc… and on Solaris - you could do a “reboot --r” - and it would “reconfigure” itself (e.g. you just added a new LUN on the SAN, and the server wasn’t seeing it)
Mostly these days - I just use “halt”, or “reboot” - however I’ve noticed some anomalies… “halt” doesn’t always halt the system.
Tonight I just finished patching 7 x Oracle Linux 7.2 servers - production… when I was doing the dev and test and training environments a few weeks back - I noticed “halt” wasn’t powering them down in VMware ESX… so tonight I tried “shutdown -h now” - and that worked - so I’ll use that in future… but I prefer “halt” because it’s less typing 
I’m aware that many of these variations are just aliases to other commands…