An air conditioner cannot create cooling, it can only relocate the heat. This heat is removed in two ways, as an actual temperature drop, and as water. The refrigerant carries the heat outdoors where it is discharged: while the water, called condensate, is collected separately and pumped or drained away. When installed properly, most air conditioners perform these operations automatically. The exception to this is the portable air conditioner, which must be vented and drained by the user; but it is these features which give the portable air conditioner its flexibility.
There are two types of portable air conditioners. The first or "evaporative" cooler uses water to relocate the heat. This type of portable air conditioner is primarily effective in dry climates, as humidity is a byproduct of the cooling cycle. This type of portable can often be found in 12 volt models that adapt well for use in cars, campers, boats, etc. The second type of portable air conditioner uses a refrigerant and is very much like the standard window unit, except that it usually comes on wheels and is meant to operate on the room's floor. They plug into a standard 120 volt outlet, and a "vent" must be installed through a nearby window. A condensate pan must also be dumped periodically, when in use; although some models also exhaust the condensate through the window vent.
Developed mostly for commercial use, the portable air conditioner was designed to supply extra cooling to temperature sensitive areas during extreme weather conditions. They are quite useful in protecting equipment and inhabitants from over heating when the temperature demands overcome the building's permanent HVAC system. Residential versions are now available, and can be used in many applications where cooling is desired.
As mentioned earlier, with little installation effort, they can be used in the garage, barn, camper, enclosed porch, etc. You can watch TV with it in the den, then take it to bed with you at night. Even though they are portable, cooling is a slow process, and when the unit is relocated, it will take time to condition the air.