Good points. I have belived in the same concept that stretching while semi-erect will be more beneficial to length than when done flaccid.
My whole length routine is done semi erect now and I feel a GREAT stretch VS flaccid work and the feeling of gaining while doing this is much higher than ever before.
When we have a erection, semi erect or 90% etc and start stretching it, we are stretching the spaces in the penis filled with blood and makeing them longer than normal ... this wont happen when flaccid, the tunicae isnt going to get hit as much even in the angles that hit it such as certain hanging exercises ... gains do happen, many guys proof of that here BUT if done semi erect I think more length gains will come about.
Look at the girth gains concept and wet jelqing ... get erect and jelq, which engorges the penis and milks it over and over with more blood and in time the penis grows back thicker and bigger .... if done flaccid it wont grow back thicker, but reports of flaccid length have been reported ?
I cant comment.
So yes, erections while stretching for me make GREAT SENSE but I feel newbies should stay well away until they can do Penis Enlargement with good form and know their own limitations and what sensations mean what during the exercises.
I will say that expressive stretching done semi erect is AWESOME and I can see much of my inner penis comming out from that.