Freehold is a perpetual form of ownership. Buying a freehold property, you become the full owner. You can freely dispose of your property, that is, give or sell, inherit or rent. Since the freehold is not limited in time of action, you do not need to renew it, unlike the leasehold.
But according to Thai law, a foreigner cannot own the land in freehold. So the right of free property applies only to the building (if it is a villa) or apartments (if it is a condominium).
The main disadvantage of freehold is its cost. Property with full ownership is always a bit more expensive. But the main advantage of this type of ownership will be that when you choose a freehold, you can be absolutely sure about your property!