My wife is 35 weeks pregnant and I go with her to all her OB appts. If we didn't put it on a shared calendar, someone is gonna miss it (though to be honest it'd probably be me, which isn't the end of the world).

We almost never schedule dinners, but we buy cinema tickets ahead of time (or concert tickets, or whatever event). Those ones are hard to remember because the show may be at 6 but doors open at 5 so lots of stuff needs to be coordinated.