Decided to paste the change log entry here for easy reading:

CLARIFICATION ABOUT STAT AFFINITIES

Just to clarify things, the main adjustment made to this feature was the daily stat task. Instead of having a chance to fail a task, you now just have one less task to do in your weak stat.
The pet and quest affinity systems are the same, so they do not remove stats you already have. The -1 means that you have a chance of getting +0 in the stat you're weak in if the quest/pet food gives +1.