One of the Merriam-Webster definitions for cumulative that is most appropriate to massage is "increasing by successive additions". You might not realize it, but massage and exercise are very similar when it comes to consistency, frequency, and results. The more and consistent you exercise, the better the chances of meeting your exercise goals. Depending on how often you exercise is directly related to the specific activity goal(s).
The same can be said about massage. Research tells us that a massage once in a blue moon, while nice, is not very effective. The benefits of exercise and massage are short-lived. The likelihood of increased benefits is directly related to the frequency/regularity of your massage sessions. This is why massage therapists note the cumulative effect of regular sessions. From a physiological (body) point of view, massage affects the cardiovascular system by dilating blood vessels, which promotes circulation. More consistent, frequent, successive sessions equal better circulation. The Journal of Sports Medicine and Physical Fitness points out that psychologically (mind), massage can reduce stress, tension, and anxiety - enhancing relaxation by activating the parasympathetic nervous system. More consistent, frequent, successive sessions equal a calmer state of mind.
It is also important to point out that the cumulative effect of massage depends on your schedule and finances - I offer 30, 45, and 60 minute packages that can fit your needs. When thinking about your goals, consider consistent, successive massage session additions!