Granting exclusive use to a lot should not just involve passing the relevant motion it should include a financial contribution to the Strata from the lot owner who benefits as depending on the amount of land involved will increase the value of that lot significantly. Remember this transfer is permanent and cannot be reversed without the lot owner (and subsequent lot owner) agreement.
You need to work out the value of the land / sq m and then multiple that by the land being transferred. Take for example an extra parking space transferred from common property you could expect approx $10,000 depending on where the land is.