Trends are trends, but first of all, you should not forget who you are making the product for. Using such a temporary concept as a trend, it is not always possible to adapt it to a long-term thing. What may look cool today will be outdated a year from now. Therefore, the client may have to change the brand book or what you have been working on.
But trends are very cool for something temporary. It can be some kind of event or festival, where emotion is important, not systematicity. For example, the Molodist film festival changed its identity every year to be different.