Board Thread:General Discussion/@comment-188.83.87.210-20150321080032/@comment-2045890-20150325092913

Tiles that drop down from the top of the board are randomly generated, supposedly with equal chance between all the tile types, so 1/7 chance of receiving each color or a team-up tile.

The AI will always prioritize match-4's, thus the decision to take a match-4 yourself or make a cascade elsewhere will typically depend on the color of that match-4. If the color is not one that the AI can use for a power, and the board is sufficiently messy that the AI is unlikely to generate a big cascade with that match-4, then you can consider making a separate cascade and let the AI make the predictable move. Typically you'll be better off making the match-4 yourself, or you can create a cascade elsewhere that will move enough tiles to prevent the AI from taking the match-4.