It depends on how you use sex to help you project. I would say that it can effect projecting in one of two ways. First as you have mentioned it can help with relaxing if you release your energy, and ejaculating can cause you to feel relaxed, drained and disconnected from your body. But at the same time it can cause you to be too relaxed and fall asleep. From your post I assume that you do not know about Toaist sexual practices and cultivating sexual energy. In this practice you pull your sexual energy through your body and store it. This not only leads to better feeling sex it also makes you more energized. To me this can help you feel your energies bodies better, which when trying to project can help you move your consciousness more easily to your astral body, and not feel drained while doing it either.
Is sexual activity, in the physicial world, related with the energy needed to experiment an obe?
It can take some energy away but it could help to relax in a great way. What do you think?