It can be troublesome when the upper left hand corner has no more candies to combine. And if that happens, your only hope is to wait for moon struck or make special candies, and they are somewhat hard to create.
The unstable moon scale compounds the problem of activating special candies.
Each moon struck only lasts for one move which limits the safe period of activating special candies. This can be a problem when combined with the unstable moon scale.