So some more thoughts on this. I Googled "ejaculation prostate cancer" to see what the actual research was.
Apparently, there is a largish study (32,000 men over an 18 year period) that shows a correlation between frequency of ejaculation and lower risk of prostate cancer.
However, correlations prove nothing about cause and effect, they can even just be coincidences.
There is no robust theory as to why frequency of ejaculation should lead to lower risk of prostate cancer, and apparently there is even at least one smaller study that shows the reverse.
Age may also be a factor that was not tested for in the large study mentioned.
There are also differences between ejaculating when having sex and when masturbating that have not been studied.
So the answer as to whether frequency of ejaculation leads to lower prostate cancer risk is far from proven.
On the other hand, if it is true, one theory is that it flushes out harmful chemicals in the semen, which would cast doubt on my "injaculation" theory maybe.
The Taoist theory of injaculation is based on the idea that semen takes a lot of energy to produce, so keeping that energy within the body to be reasorbed should help to stop energy depletion. However, the concept of energy is used in a manner that may or may not be interpreted within the so called Western scienific framework, so to some extent it depends on which framework you buy into as to whether you have faith in the theory.
Further, I have read another possible explanation for the root of the Taoist practice being as a means of birth control, which was important to the upper classes who were concerned about heirs and so forth. This obviously has nothing to do with individual health.
None of this says anything about mental health, which as we all know, is one of the main reasons many of us are using this site.
So I still don't know the answer to these questions, other's knowledge or thoughts are welcome.
Thank you.