Maybe if you want to heat a subset of rooms for the cost of heating the whole house.
Electric heaters are extremely expensive to run relative to gas or heat pumps.
Heat pumps are great and extremely efficient, but not they are as hard to install as air conditioners (because they are air conditioners that work in reverse).
Windows here in Europe don't usually slide. And in Europe we like looking out of them :)
But heat pumps are also available in single units now. They're getting quite popular because they can be self installed (no refrigerant engineer necessary).
I believe there are models of window units with heaters available though they may just be doing resistive heating. I've seen plenty of mini-splits running as heaters obviously using heat pumps and they seem to work quite well.
Electric heaters are extremely expensive to run relative to gas or heat pumps.
Heat pumps are great and extremely efficient, but not they are as hard to install as air conditioners (because they are air conditioners that work in reverse).