Yes, for lower level players. In general, your ghost performance is going to be the same as your pecking order in the pool hall.
Some exceptions, for sure. There are some people who crack under gambling pressure, but do great practicing solo. But, these are exceptions.
A players, will mop the floor with the ghost, and C players, won't ever beat it in their life. B players will win some sets, and lose some sets. D players, won't even get to the 2 ball in most of the racks.
Now, at A and above, it is probably not that useful. An A might beat it 7-2, and a touring pro might beat it 7-1. Its too easy to show the skill difference at high levels. But at anything under an A level, I think it speaks volumes.
As mentioned earlier, it also only measures offense. But, usually, a players entire game will come up at about the same rate. As their offense improves, so does their defense. Their position play. Their kicking. Their breaking. Etc. Again, there are exceptions, but most players I've played have a reasonably in-balance game.
PS, all the above is for the 9 ball ghost.
IMO always
