Often people gain well on the Newbie Routine, then after 3 months or so they try different things and their gains grind to a halt. When I ask them if they carried on warming up with the new routine, usually they realise their gains stopped about the same time they stopped warming up.
I frequently get lazy and don’t warm up for a while; I look on these times as fine for penis health, but I know I won’t get much growth without a warm up. Once your penis is ‘conditioned’, the warm up becomes even more important, as the tissues are slightly tougher and more resistant to gaining.
Some guys can gain without a warm up, but they still have a slightly higher risk of injury, and could probably gain faster if they did warm up properly.