i don't think it's harmful but alittle too much of it might.
I've been doing nofap since a couple of months now and when i relapsed after 15-20 days i didn't feel as bad when i was fapping every 2nd day to (pornographic stuff) so trust me it's not the usual fapping that destroys you it's mostly pornographic stuff (i was too much into doujinshi).
nofap has helped me eliminate ALL of what's pornographic ever since i started.
my goal now is 30 days no fap, when i reach the 30 days I'll go for 90days.
then I'll decide what's best after, but atm.
i love being on nofap, i noticed that when i fap (you sometimes then binge it's dangerous).
when this happens, i lose focus.
and things become abit more difficult to remember etc.
fapping at the end of the day is completely normal as long as you dont stick your eyes to co**s and vag*** all day long.