
Every class and every job actually has a complete hotbar 1 through hotbar 10 and crosshotbar 1 through crosshotbar 8. Then there is Share which is a complete set of hotbar 1 through hotbar 10 and crosshotbar 1 through crosshotbar 8.
When you turn hotbar sharing on, the Share for that bar becomes active and hides the job-specific bar. When you turn hotbar sharing off for that bar, the Share bar is hidden and the job-specific bar becomes active. You can take advantage of this in many ways, not the least of which is macroing draw/sheathe weapon with toggling the share state of several bars, for example
Code:
/mlock
/battlemode
/hotbar share 1
/hotbar share 2
/hotbar share 3
which will draw/sheathe your weapon and simultaneously toggle bar sharing for 1 through 3. This allows you to hide your job-specific bars until you're ready for combat, and when you're out of combat you can use the same bars for general things that are only available outside of combat like mounts and teleportation (or just make your bars invisible outside of combat, if you don't put anything on the shared bars).