I agree that snagging should be done before hand. I however notice that developers are not keen on doing this until the contract has been notorised.
I also understand that lack of snagging does not allow the buyer to not to complete, (surely until you are witholding the completion you have some kind of influence on the developer and if the developers has to do the snagging why cant he do at the time. The buyer is satisfied and happy)
another quirk of Spanish law.
Further, many of the new builts will not have water/electricty so items such as plumbing,electrical/TV connection etc, cannot be checked.
In my property the developers has been in and out at least six times for the same thing. I cant see why it could not be done propery in one or two goes. Maybe the sub contractors are paid by the visits they make.
In my experience the developers have no concept of quality control and in the case of a very large developer from Galicia, who does not even have a after sales department.