When I go on vacation for a week there is no way to say "go to max energy savings while saving my pipes mode until just before I get back." I can reprogram the entire week, but then I lose what is the correct programming for normal until I reprogram it. Worse my house is uncomfortable when I get back - usually when I'm tired and want to jump into bed asap (if I know I'll get home about noon I'll look for a tourist thing to kill some time long before I get home).

I don't always have the same schedule. When I'm home sick I don't want to reprogram it. Some weekends I'm at home all day, some I'm out all day - which program is right? IoT thermostats also through privacy and reliability concerns in. The old fashioned mercury thermostats from the 1950s still work as good as new. While your IoT thermostat work next year - some do not.

All the above is made even harder because my house is headed by an air source heat pump: if I'm returning at 9pm it might or might not be better to start heating my house at 11am when the day is warmest. The algorithm depends on the weather which is best predicted the day of.