I was a very early adopter of programmable thermostats (we didn't call them "smart" back then). We installed a Honeywell Chronotherm III in our condo c.1989. We did not live there long, but I was very happy with the functionality of the Chronotherm.

Since then, I have owned 3-4 programmable thermostats. None of them have had as satisfying a UX as that old Chronotherm. Why? The Chronoterm had 1 key function:

Skip Next Period

Very common use case. You are home sick for the day, and don't want the temperature to go down, like it is programmed for when the house is unoccupied during the workday. Or you have houseguests, and don't want to inflict your penny-pinching overnight setting on them.

Change To Last Period

Also very common. The Skip Next Period use cases above apply, except if you aren't on the ball and forget to choose SKIP in advance. Or you get home from work early. Or have insomnia and wake up early.