Board Thread:Question and Answer/@comment-190.145.72.86-20141204172251/@comment-25000380-20141211031927

When you lock a card you'll be unable to use it as upgrade material, sell/medaled it & Awake the maiden (and even maybe evolve the card -not sure, haven't tried yet)

It's good to lock cards that you want to keep in your collection, that way you'll not waste it by any possible mistakes.

<( ^•^)/