It states in the skill tree "One more move to collect a candy on puzzles". The way i understand this seems to make this skill a PitA. It would take 1 more moves to get a candy?
I got the skill after much progress in the game and i now understand what it does.
It allows you to see in advance what is the secret candy's requirement. So having it level 1 is really helpful if the requirement is based on a number of evidence. When it is based off clues, it was already pretty simple.
Getting more than a level is IMO useless unless you have finished the game and have nothing left to spend on as 2 moves is more than enough to get practically any evidence...