Most? Essential? Not really. I can hop into most of the channels with a different nick every time. Nobody cares. I can even use the same one without registering it as long as nobody else does that. I can open a chan without being registered and enforce rules in there.

The only time I need to register something is when I want to keep the channel alive and still be OP when I come back, when I want to keep my nick or when the chan owner requires me to register.

Which is all not "most channels".

Some channels ban non-registered users to protect themselves against spam.

You don't need chanserv and you don't need nickserv. Efnet isn't dead -- it's just coughing up blood. (yes, it has ChanFix).