In the heat of the summer, even a carefully replaced divot can quickly shrivel up and die. So, in general, during the hot weather, you're better off filling that crater with the mix.
However, during the shoulder seasons and in the winter, often the best decision is to replace the divot. With cooler weather, there is a good chance that a carefully replaced divot will survive and knit back into the earth. In addition, with cold temperatures, there's little likelihood of the seed in the divot mix germinating, so divot replacement is going to be the better choice.
Of course, when some players take a divot, it explodes, and can't be replaced. In this case, even in the winter, go ahead and smooth the surface with some divot mix, instead of leaving the point of detonation unrepaired.
Remember, the Rules of Golf do not allow you to move your ball out of a divot hole without penalty. So, as you would with a bunker, please repair your divot in the way that will provide the best surface for those players who come behind you.
|A replaced divot, healing in nicely.|
|A divot that has been properly filled with mix.|