My part of the house is long and skinny, with rooms branching off a hallway, and a single split system at one end. It's not really up to the task on extreme weather days and I find a fan halfway down the hall to push the cool air into the end rooms is essential. I also have to get this going before it's really needed, because if I wait until it's hot to turn on the aircon it doesn't cool the place down at all.

In winter when it's extremely cold I have to have an extra heater in the hall to blow some heat into the end rooms when necessary.