Portable air conditioners can cool an individual room instead of the whole house like central air conditioning does. Cooling unoccupied rooms could be wasteful. Though in places especially like Florida where there’s more humidity it is best to cool and dehumidify the whole house anyhow regardless of being occupied. You want to always keep the house dry and mold free. Still in a lot of places it’s not really necessary to always have ac running through the entire house. Cooling just rooms while occupied can save money on electricity bills. This can be done with mini splits and window AC’s as well.