by piousflea
At least with the current enchantment design, it is not that difficult to tell if an enchantment was cast illegally.The enchantment target line requirements are all things like "Non-Mage" or "Living" or "Zone" which cannot be changed on the fly. There are no enchantments that target temporary or removable keywords. (such as Flying, Wounded, etc.) Therefore if the enchantment was cast illegally, it will still be illegal when it is revealed.
Casting an improper face-down enchant could definitely be of major strategic advantage. Imagine someone who's already used up all their teleport traps casting Chains of Agony face down on a zone to discourage their opponent from moving in. That could totally swing the momentum of a game.
In a tournament setting, improper use of Enchantments can and should be a serious infraction. (for a less competitive tourney this could be a warning followed by game loss, for a highly competitive one it could be immediate game loss or disqualification)