Do you think small, yappy dogs are of any use? Some people just can’t have a big dog (or more big dogs), yet a few yappers who would fly off the porch and make a ruckus could fit on the roster.
Better than nothing and part of a plan, I suppose.
Small dogs are great, especially if they are trained (or it comes natural) to always alert anytime anybody approaches the house from any direction. Their hearing can be many times better than yours, giving you time to react and get armed.