Look at it this way - everyone is different and needs different stimulation. Some females cannot cum without direct clit stimulation, but some can cum from just nipple play. If you can become aroused and wet from words alone, it would not take much 'practice' to also get you to also cum from words alone, and then it becomes a simple matter to make it 'cum on demand'.
I disagree with the previous poster about the 'quality'.
O-Control is my kink. Having taught someone to cum on demand, there are many variations that can be added. For example:
"Get on edge for me - but don't cum"
"Have a small O for me now"
"Have a big O for me now"
"Cum for me now, and don't stop - you will keep cumming until it hurts, and then even more"
And for the really cruel Master:
"Cum for me now" and the moment she starts: "STOP cumming immediately!!"
(Listening and watching her struggle now is amazing)
The 'quality' of these O's are very different to ones from masturbation or sex - they come from the mind and submission. To have another have control over a very private and personal body function is extremely powerful.
The above takes a close bond of love and trust. The sub doesn't 'make' any of these things happen - she opens her mind to allow the words/suggestions control her body.
With training and experience there is also the most wonderful experience - I call it the 'total body O'. With words and touch, it is possible to spread the arousal in the pussy through the whole body. Every part of the body feels the arousal building, tingling and need. When orgasm is eventually allowed, it is felt everywhere from the toes to the fingertips - and everywhere in between.
Altho I have had no experience in this area, it seems that it is less likely to train a male to cum-on-demand than a female. I find this strange because during pubity, it is the male that has wet dreams (hands-free) but the male seems to need a very definite physical stimulation later in life.
Brosco
PS: Please ask more if you wish. Its my favorite topic and I could talk all day
pps: Purely using O-control/cum-on=demand, I have managed to make a sub cum 30 times in 8 hours - yes, I counted.