Well it’s two pieces of the same puzzle..
Jelq (IMO of course) has the low scale benefits of:
a) stretching the existing tissue a little more everytime => gains
b) pushing lots of blood in the slightly injured tissue in order to get healing on the way
If you can find a working balance (for yourself) between a and b you shouldn’t have to stop jelqing (unless you re getting in one of those stuck-phases where the tissue needs to rest).
The tissue feels very hard to the touch (at least for me it does ;) ) so I figure it _is_ hard, meaning there’s not as much space left to push blood into the tissue than when you are only half-erect.. Could be an effect resulting from the “skin” surrounding the corpa though (which feels tougher if your penis is fully erect than when it is not).. If there wasn’t such a “skin” (let’s call it sub-skin) the tissues would just bulge around everywhere, not necessarily only your boner itself so there should be such a thing… bad reasoning from my part maybe, but it does make some sense to me :)
On re-reading the last passage I think I found a similarity to your body’s cells being stretched when warm as oposed to cold..
Could be a similar mechanism on the grandscale (and a similar one on the cellular scale).
Ys