Segmentation is one of the first critical decisions a social marketing or health communication program must make - even if it is to not segment and use the 'field of dreams' strategy ("If we build it, they will come"). Even when decisions are made to identify and focus on priority segments of the population, many segmentation approaches end up being used for no more than directions for casting calls and art directors ("We need to have one of these types and another of these types").
As I put it in Social Marketing and Social Change:
"...the purpose of segmentation is not to answer the question of whether we can distinguish different subgroups of a larger population. The question for segmentation is whether identifying differences among groups will drive how we approach our marketing solution. That is, does it make sense to have different behaviors, messages, products, and services aimed at specific subgroups of people? Or are there certain common characteristics that supersede these distinctions? And just as important, if we do uncover such differences, do we have the resources to develop the specific marketing mixes each group deserves?" (p. 133)
Too many programs, maybe even yours (?), conduct segmentation research and analysis and then proceed to design one intervention to serve multiple groups. That is not good practice. Other efforts are more academic in nature, and seek to understand what characteristics distinguish different segments from each other, but offer few insights into what those differences mean for marketing and communications (other than broadening or narrowing the casting call).
There are people who will argue with you that segmentation goes against the grain of trying to serve everyone. You might counter these opinions by referring to a recent study that examined the ethical dimensions of segmentation and found there is more potential harm from not segmenting - specifically that mass approaches (or "one size fits all") can actually deepen disparities among population groups (a point Dick Manoff also made many years ago).
Newton JD, Newton FJ, Turk T, Ewing MT. (2013). Ethical evaluation of audience segmentation in social marketing. European Journal of Marketing; 47:1421-1438. [Abstract]