Graham
Always a good question
If someone phones me and asks to learn this art I always suspect they are a fruitloop and 9 out of ten are, that is why I only usually teach it to senior students who I know are interested and I certainly don't 'sell' this art. I mean why would anyone choose to dangle something off their cock?
The reason I took this up is simply that this the major way my teacher got his power, health, strength, vitality and seeing what he had (despited at the time being three times my age) I wanted it! I would never have dreamed of doing it or have sought a teacher out to learn such a strange seemingly 'fettishy' art if I hadn't seen the results on my teacher and my seniors and already 'known' them. Of course being involved with this art immediately (and understandable) means many presume you are a bit, well, weird
.
However some of the main benefits I attribute to it are:
i. Body hardening - within 6 months of taking it I could take an ungloved punch to the torso/limbs without bruising or pain from 95% of people.
ii. Health - I hardly ever suffer any illness and haven't visited a doctor since a decade ago when I learn't it (except for injections when travelling) - I a not naturally one of those guys who never gets sick.
iii. Dantien Power - think of squatting monkey with weights! Okay perhaps a poor comparision as I have never practiced that skill. But is certainly imrpvoes power generation.
iv. Strength - I found my strength increased significantly (even though all my other practices remained constant).
iv. Vitality - This is the main thing I noticed, my required sleep reduced by about 2hrs a night and my recovery time after exercise went right down. You just feel very very good.
(it should be noted I wasn't new to qigong/neigong at the time so it wasn't the 'first flush' of energy work). There are other ways of achieving these things but for me Shi Shui worked well.
It should also be said that it isn't a painful practise (if it is your doing something very wrong) or uncomfortable and is quite an enjoyable. Nowadays (over a decade later) from a Taoist Energetic perspective I find if I skip it for more then a few days my meditation, will power and martial arts suffer - it feels like I have less 'gas' to fuel whatever I am doing.
Hope this helps explain a bit:) .