I do not work in the "pure" advertising field, but to me, product personality covers the associations consumers have with a product, and representing the product with the "correct" personality means you are more likely to reach the right consumers. Understanding product personality is important because although you do have the occasional "breakthrough" ad which uses a wild angle to sell a product, a misunderstanding of product personality can lead to disastrous results. You could expect to market an athletic shoe using a sports figure, young people having fun, etc because that is the personality of the shoe: It is for active people having fun. You could (probably) not market coffins the same way because the personality of coffins is completely different.
