We have fairly new heat and AC systems. Both are infinite speed, generally running extended periods of time but at very low power, and cost, and high, steady comfort levels. Heat is set at 69, AC set to 76. Whichever is needed, that's the one that runs.
We might temporarily adjust if coming in from the outside and it's very cold out or very hot out and we're looking for a warmer or cooler feeling for a short period of time.
As for who, either of us adjusts if needed/desired. I have app on phone, Marie doesn't want it on her phone. Marie won't set thermostat lower or higher if leaving the house for an extended period of time. I will, if I remember, which is most of the time. If I forget, I'll raise or lower from my app, when I remember. Maybe 30 minutes before expected return home, I'll reset from my phone. Like now, neither of us are home. Heat index here today is at 106. I have thermostat set at 80. Before we go home I'll drop it to 76. When we get home it will be 76.