One example for me is iproute2 (includes the ip command, which as I've heard is the successor of ifconfig in Linux). Looking at the manpage right now, it seems to have improved over the years, but it's still lacking. For example, if you look at the manpage ip-link(8), there's a large list of possible types of link interfaces, but if I pick one I don't know like "ipvlan" and search for it all I'll find is a brief description saying "Interface for L3 (IPv6/IPv4) based VLANs". That leaves me with little idea on how it can be used. I've learned to use "bridge" and "veth" from examples I've found in the wild, but I don't think I would have from the documentation.
EDIT: Removed scare-quotes in word successor.