Most operations have a route book whether they call it that or not. The difference is whether anybody maintains it.
Why it matters
Recurring work is the majority of the calendar in pest control, and recurring work repeats. A decision made once in the route book is a decision made 12 times a year. That is leverage in both directions: a good lane assignment pays out every month, and a bad one costs every month until somebody notices.
A stable book also absorbs shocks. When a technician is out, the question is “who covers this lane” rather than “who can take these 47 unrelated jobs”.
How you notice it slipping
Dispatch rebuilds recurring work by hand each month. The same customer sits on a different day each visit. Nobody can say which technician owns an account without opening three screens. Cancellations create chain reactions, because there was no structure for them to fall back into.
What to do
Treat the book as governance, not setup. Assign ownership before you assign stops, keep one weekly slot for cleaning up drift, and measure how many recurring appointments moved lane in the last month. Software can hold the structure; it will not defend it for you.