A ghosting sail will be very light cloth, possibly spinnaker cloth.
It will stretch out of shape if you use it in much breeze.
It may be cut for reaching rather than upwind.
Not so common these days, too many headsails penalised by rating rules?
There may not be one answer, but I believe a ghoster is just made of a much lighter weight cloth so it will set in light winds whereas a general purpose genoa will be too heavy to hold it's shape. I use mine in winds of f3 or less only.
The ghosting sail goes 'pop' as soon as the wind gets up.
On a more serious note, true ghosting sails are cut fairly flat as in true ghosting conditions, any great shape in the sail means that any chance of laminar air flow is lost.
My 40 year old Ghoster is a spinnaker weight 150% Genoa. I use it from a broad reaching to up to 50° off the wind in winds under 10kn. I don't have a pole long enough to pole it out for running and by the time the wind is strong enough for it to keep its shape on a run, its time to drop it before it gets strained or rips.
I set it loose luffed and had the wire luff rope replaced by Dyneema this winter. The sailmaker said it had a good few more years in it if I kept it out of the sun.
It gets used half a dozen times a year as a stopgap between my Yankee and Staysl foresail combo and my trusty Yanmar. Any significant waves shake the power out of it at much under 5 or 6kn of wind so it has a very narrow band of conditions that its useful for.
It was a sod to handle too, until I took the snuffer off my (never used) spinnaker and put it on the Ghoster last year. Its much easier to set and lower now so might get a bit more use. But not much more
Modern Code Zeros and cruiser chutes are probably more useful but, like you, my Ghoster came with the boat and is only costing me storage space that my wife wants for beach brollies and a yoga mat. I'm standing my ground on Offbeat being a sailing boat and needing more sails not more clutter!