What is the advantage to playing a deck full of cards with locking abilities?

Locking does not only stop damage-over-time abilities, it stops any other abilities that a card may have. This may include effects like:

• Resilience: locks stop resilience so units do not carry over to the next round (good against e.g. dwarves).
• Buffing: some units get buffed every time something happens (e.g. Skellige axemen). Locking them stops that.
• Consuming: locking stops consuming from happening.

This means that locking disrupts the core strategy of certain decks. For example, dwarf decks usually depend on carry over units so locking their big units prevents them from executing their win condition.