I regularly use practice mode after building a new deck to quickly get a feel of whether it's working as intended or not. It would be very helpful if we could set the deck and champion that the AI plays against you in practice mode. Currently most of the practice mode decks are pretty weak. It would be great to see if a new deck can survive the pace of a current aggro meta deck or go under a current control deck to see if you need more tuning before you play it on the ladder.
"Ignorant beliefs are stains upon the mind."