Convenience is relative. Whenever I hear an ad touting the "convenient location" of the establishment being advertised, I have to chuckle. I think of a "convenient location" as a place that is quick and easy to get to, and I assume a place advertised as "convenient" is probably located near a highway. Though a store might be right along a major thoroughfare, if it's 50 miles from my home, it is not convenient to me.
I've often heard Watertown residents cite its convenience as one of the reasons they like living here. I assume they are referring to the town's proximity to Boston and access to public transportation and roads that go into the city. They may also like the Mass Pike being a quick ride from their homes. But though I like the fact that Watertown is close to Boston, I don't find the town to be convenient, either to going in town or to traveling elsewhere in the metro area.
Because both the Pike and Storrow Drive provide direct routes into the city, we have easy access to Boston by car, but the volume of traffic and the cost and difficulty of parking often preclude driving into the city. Fortunately, you can take public transportation from Watertown to downtown Boston, but unfortunately all routes involve buses. I've lived both in Porter Square and outside Davis Square, and I found those areas to be extremely convenient because I could walk or take a quick ride to a subway station, then go directly to my urban destination. I find that a bus added to the route, as it is in Watertown, causes much inconvenience, involving both comfort and timeliness.
Since the buses travel on streets full of traffic, the ride is much slower than the ride on the subway, with its dedicated tracks. The bus also makes more stops. Because of these factors, a bus commute is longer than a commute on the subway. On several Watertown routes, buses are scheduled to leave every 15 minutes or so on weekdays, with trips a bit more frequent during rush hour and less so later at night. On weekends, the buses travel less frequently. And no matter what the schedule, buses have a habit of being late.
Subway stations are not exactly comfortable environments, but at least most of them are indoors. Waiting for the bus involves standing outside, often with no shelter, for long periods of time. For a good part of the year here in New England, that is not very pleasant. It's no fun to stand around for a long time when it's really cold, extremely hot, raining, snowing, windy. And of course, my bus stop is on the cold side of the street
The 73 bus on Belmont Street runs more frequently than the 71 on Mt. Auburn Street, which of course is the line that I take. There have been many occasions when I've been waiting for the bus at the Harvard Square station, and several 73s – up to six – have come through before one 71! The last time that happened to me, when the 71 finally arrived, it seemed like two busloads of passengers were packed into one bus, which made for a cramped, unpleasant, and very slow ride. When I finally got off the bus, of course there was a nearly empty 71 bus coming along behind.
I find Watertown even less convenient when it comes to going places beyond the Boston area. The Mass Pike is the only highway that is close to Watertown, and its disadvantages include the costs in both money (the tolls) and time (the line of traffic that often backs up at the toll booths). You can reach locations west of town via the Pike, or you can head east on the Pike and drive through Boston to go south via the Southeast Expressway. (The latter is a long and arduous ride in lots of traffic.)
Route 128 is one of the main travel routes in the Metro Boston area, and Watertown seems to be close to the center point in the land that the highway loops around. If I have to go somewhere that is located on Rte. 128 in Waltham, I ignore directions that cite which exit to take from the highway because it's easier to just drive through Waltham to get there. You can take the Pike or Route 2 to 128, but neither are quick trips from home. Other highways in the state are even further away.
So as I said at the beginning, convenience is relative. I don't consider Watertown to be convenient, but your mileage may vary.