In many cases the solution in the back of the book is a factored form, and from what i understand. A factored answer is preferred, so i have just been doing it lately out of habit.
But I don't understand why this is needed in many cases. I do see that it provides a simpler answer in some cases, but in quite a few other answers the complexity of the answer is higher with the factored version.
So my question is why is it preferred?