Route optimization is the practice of automatically reordering a crew's daily stops to minimize total drive time across the day. For lawn care, that means looking at the 20-40 customers a crew has on the schedule for Tuesday and figuring out the most efficient order to hit them — accounting for street layout, one-way roads, and where the crew starts and ends the day.
The difference between optimized and unoptimized routes is usually 30-60 minutes of windshield time per crew per day. For a 5-day-a-week crew, that's 2-5 hours back. For a 3-person operation running multiple crews, it can be the difference between fitting in 5 more yards a day or hiring another truck.
Most modern lawn care software does this automatically. You add a stop and it slots into the right place in the day. You add a one-off visit and the route reshuffles. The good implementations are invisible — you don't think about routing, the crew just gets a sequenced list of stops for the day.
Legacy software (and most spreadsheet-based scheduling) assumes the operator manually orders the day. That works for 5 customers, breaks down at 30. Once a crew is full, route optimization is one of the highest-ROI features software can offer.