I use the ghost as a stand-in for specific levels of opponents I expect to face; usually when I'm going to gamble.
If I'm playing somebody who shoots well enough, but can't jump at all and rarely makes contact on all but the easiest of kick shots, then I assume the ghost will make any shot that isn't obstructed. Of course I want to play lock up safeties, but practicing adequate safeties for the level of opponent coming up is still of value.
When preparing for playing a great player giving me weight, I take that weight from the ghost. I'll judge my safety play and determine if I sold out to the ghost based on the upcoming player's ability... I assume they can make anything they can kick at or jump, otherwise I take BIH and continue.