The idea it that if I have a few containers that need to know each others. Say an application server `app` and a PostgreSQL database `db`. While conceptually I need to spawn only `app` and `db`, I have a script to actually spawn `ns` (i.e. dnsmasq), `app`, and `db`. That script will register the IPs of `app` and `db` into dnsmasq (as you describe in the post).

This means that I can run that script more than once on my laptop and have multiple triple (`app`, `db`,` ns`) side by side without fear of crosstalking between logical groups.