Each location has its pros and cons. Outside installations may compromise some of your privacy, but you can add screens, shrubbery, or fencing to minimize peering eyes. The outside weather can be a deterring factor, although many people absolutely love the experience of lounging in bubbling hot water while a light rain or snowflakes are falling! It can be exhilarating. Awnings can be built to shelter the effects of weather. It should be noted for those of you who have not experienced it, hot water raises your body's core temperature, so you will normally not feel cold even when exiting a hot tub outdoors in the dead of winter.
Inside installations will add humidity to the air in your home. It is imperative that proper ventilation be maintained to control this moisture and to prevent mildew and other damage. If you decide on an inside installation, be sure to take into account the draining and filling of the unit. There are two other important questions: will it fit through your doorway, and is your flooring strength adequate? Keep in mind that a typical 3-person spa weighs about 2500 pounds filled with water. On the plus side, you will have privacy and convenience. Your unit and cover will also be fully protected from the weather.