It may take years, but sooner or later this will lead to a breakdown in function. However, it is not so much your organs that directly bear the brunt of a slouching squash or a straightening squeeze, it is the flow between your organs. If there is ongoing distortion and pressure you are sitting, not at all figuratively, on your metabolism and squeezing the life out of yourself. It is easy to appreciate how constriction and compression of the container can adversely affect the health of your organs and your state of vitality. It is not always so easily appreciated how lack of flexibility is its accomplice.
Respiration is the best example.
Breathing is the most noticeable rhythm in your body. One of the most common of interfering habits, right up there with bad posture, is good posture. Bad posture most often means some version of slouching or collapsing forward with obvious consequences of cramping and jamming up your breathing. Good posture is usually the opposite, with attempts being made to straighten up and lift your chest, pull your stomach in and shoulders back and all that. The way most people get their chest up in the front is to pull down on their back with those powerful muscles that run up either side of the spine.