Sometimes it is extremely important that your information be current. It is always a good idea to get the latest research on any topic but sometimes information gets outdated.
For example, an old book on the "Dialogues of Plato" can be just as relevant today as when it was first written. It is a good idea, however, to get some new materials in addition to older materials for such a subject.
In contrast, unless one is resarching the history of gene therapy, a book on gene therapy that is even a couple years old may be too outdated.
Keep in mind, it takes years to publish books and months to publish articles. The information contained within them will be older than the publication date.