I have a cottage. We keep it at 57F when we're away. When we're there, it's 72F during the day and goes down to 68F at night.
The problem is, it takes a while to bring the house from 57F to 72F when we arrive in the middle of the day... The furnace is good and the air temp is brought up pretty quickly, but there's a lot of heat mass in a house so it takes a while before the floors are toasty, the toilet seat is not ice cold, the couch cushions are warm, etc... So I have a remotely accessible thermostat (RCS TR60) that I can send commands to via some crafty python and a cellular modem. I set it to 72F in the morning and by the time we arrive, the house is toasty warm and ready to use.
Sometimes I forget to re-set the thermostat to 'away' before we leave. It's nice to be able to set it down to 57F remotely too...
The additional benefit is I can remotely monitor the temperature and furnace runtime to get an idea if something's wrong, like my pipes are about to freeze because the furnace blower has kacked; or a bird has broken a window and now the furnace is running pretty much continuously (that happened)...
Maybe it's an isolated use case, but we appreciate it. And because the code is mine, it's not all cloud-connected and vulnerable.