This may not sound particulary useful to those US denizens where one transmitter covers practically a whole state, and is the only source of that station

Maybe those tiny little New England states or those flat ones in the west... I can't hear Harrisburg, let alone Philly, in Pittsburgh. Likewise as I go east I lose Harrisburg stations before I get to Philly.

There are some places I know of with simulcasting but there tends to be heavy overlap, which I find annoying; I don't want to hear the same thing twice, or 3 times as is the case in one place in the southern tier of New York.
So if you hit a tailback, you can switch on TA, and you'll get the next local announcement - regardless of which station you are listening to
We're getting more and more HARS beacons in the 1610-1640AM range, so in many cases that's what I'd want, and I doubt those transmitters even support RDS-TA.

On my way to the empeg meet I was in my non-tuner-equipped vehicle (at the time) and wishing I had one when I hit a backup on I-70. I ended up assuming accident, getting off and going around that one exit, and it worked out fine; I didn't see a HARS beacon sign, either, but I would have tried...