In Boston, for a long time you got a free subway ride if you left Logan on the Silver Line SL-1 (tunnel bus) and got off at the last stop under South Station.

Now until Aug. 31, 2023 if you take the Blue Line subway to downtown you also get the free ride, because one of the highway tunnels (Sumner) is closed. The Blue Line train gives faster subway connections for some destinations compared with the Silver Line bus.

To recap, take a free Massport terminal shuttle 22 (AB), 33 (CE), 55, or 66 (not the eleven ABC-E) to get to the Airport station to get on the Blue Line.

Also, until August 31, 2023, going to Logan and using water transportation you can get a Skip the TSA Line voucher.

Typical trip for me: (from relative's house) bus, subway, (aforementioned) Massport bus, fly from Logan, subway and/or bus at destination airport to convention or meeting or other final destination. Reverse procedure to go home.
(Drive alone from home to said relative's house, that is a story for another day.)