One of the reasons window air conditioning units are only useful for apartments or for a single office is because of their limited reach. The only way to cool a whole house with window units is to place them in windows in every room—which isn’t always possible and blocks up so many windows you’ll end up with a perpetual twilight in the house! And even with all the window ACs, you’ll still end up with hot spots.
With a central air conditioning system, you don’t have to worry about having rooms all around the house cool. Or you shouldn’t. Unfortunately, uneven cooling still happens, and the most common case we run into is an upper story of a house that’s hotter than the lower one. Heat rises, and in the San Fernando Valley the AC may not be equipped to deal with it.