Your body needs to keep its internal temperature constant in order to function properly. Even small changes of a few degrees in body temperature can have life-threatening results. Sweating results from your body trying to cool itself. An average healthy adult loses from half a liter to a liter of sweat per day. During an intense workout or in hot environments, sweating can be increased to more than two liters per hour. Lost fluids must be restored by drinking sufficiently, since a fluid imbalance can again have bad consequences for your health. Since there are a lot of opinions to the contrary, I want to repeat my understanding that sweating does not help you lose weight permenently. Although sweating does burn some calories, I do not believe it builds up to anything substantial. Any weight loss induced by sweating is, in my opinion, recovered as soon as you drink a glass of water.
Some like it hot, not least the Finns. If you haven't already tried sauna bathing in Finland, it will only be a matter of time before someone introduces you to it. Watch out: perspiration can be habit-forming! Imagine the scene: you take your clothes off and stem into a murky room. There are other naked men sitting next to you on wooden benches. Someone throws some water on a stove and the warmth in this little wood-lined chamber becomes an inferno. The sweat is running down your arms, your flesh is glistening. Your hear gasps and exclamations from along the wooden bench. You drop your head to avoid the initial scalding of the steam.