Your commute from Medford to Watertown is a relatively short distance that will take you 15 minutes if there is no traffic. IF there is traffic though, your commute could take an hour each way or more. All routes between the two are very limited and filled with traffic lights. In between the two towns are several lakes and ponds, railroad track lines, Route 2 highway, and a huge volume of traffic. These features create some bad bottlenecks between the 2 towns. There are theoretical public transit routes but they involve buses and no direct route.
Bottom line: If you can travel work infrequently, and do so at 5am or 8pm, you will be fine. If you have to make that commute every day at rush hour, prepare for hell.