As Bryan and Buffy stated, it can depend on the field and I won't go into that for my answer. I would add a bit to Buffy's answer regarding where you are in your career. If you're a tenured professor, then it probably doesn't make much difference whether you have it on your CV or not--publications matter more anyways. But if you're a graduate student or post-doc who's about to enter the job market, then I would ask the question of "why would you not??"
For junior scholars, poster sessions can have multiple implications beyond just presenting research findings. It can be a sign that you're active in the research community, working with collaborators on their projects, and/or disseminating findings to a wider audience than the ones who read the journal that you publish your work in, even if you're not the one who presented the findings.
It can also often times be the case that the one presenting the work is not actually the one who had the lead role in the project. For instance, you can be the PI of a large project and have one of your students or research assistants go present the findings to not only give them exposure to the academic environment but also to disseminate findings without having to sacrifice money, time, and effort on your part (perhaps you don't have travel funds or have teaching obligations and can't physically make it to the conference). In this regard, the program of research is headed by you, and presumably, you played a role in the creation of the poster, so why not receive credit for it where credit is due?
Graduate students and post-docs also often times list poster presentations that their students did on their own CVs. In the long run, this doesn't help them in advancing their own career (i.e., no one's going to get a lifetime achievement award for only successfully sending a bunch of undergrads to conferences). However, in the short run for those looking for their first professor position, having a successful track record of your students presenting at conferences can be a good sign of being an active mentor (which can be a quality that hiring committees may value).
But again, in the long run, it may not be worth it to put it on your CV if there's no benefit to career progression.