On the other hand, benefits inlcude: 1. Assistance in rearing young experience in rearing young; parental genes' survival is enhanced (kin selection). 2. if parent dies, other gets help access to resources in parents' territory. 4. help in territorial defense. 5. increased foraging efficiency detection of predators, etc.
I should mention in passing that some small birds in tropics protect nests by always building near wasps or ants (Yellow-rumped Caciques). The advantage to the bird is that wasps kill avian bot flies. The birds may protect the wasp nests from intruders (?). Hornbills protect themselves from monkey predation by sealing females into nest cavity, fed by males. Females and young break out when fledged.