Enable NPN

Next Protocol Negotiation extension. See https://technotes.googlecode.com/git/nextprotoneg.html

This should reduce round-trip time (RTT) for clients, thus giving faster load times.

This is essentially a micro-optimisation to try to turn on all the switches that can make things faster.
Have you verified that client_max_body_size is correct when applied to a machine. I don't want backdrop's write API to suddenly break