It's for drying out. For a bodybuilding contest without resorting to using potentially dangerous pharmaceutical diuretics (which can have some SCARY effects if done improperly), for a photoshoot or beach trip or anytime you wanna physically look your best. Pulling water out from under you skin is gonna make you look leaner & tighter. Lower your water and sodium the days leading up to an event, cut all carbs for a couple days entirely in combo w/ depleting workouts, then smash fruits or whatnot right before and watch the glycogen stores refill, all while the water under your skin has been lowering. It'll be a darn good look. For me, I can weigh in a good 16 hours before I start lifting (about 5pm evening before) so I can cut water down to 219.9lbs or less, weigh, then start eating as much carbs sodium and fluids really as I can muster. I cut 5lbs just shutting off food/water 20 hrs before weigh in last time, no sweat cardio, saunas or diuretics, so w/ the Dry-Uretix I think even 8lbs would be a very safe bet. If I go carbless a couple days prior I could drop some glycogen weight too and prob get a better uptake the night before the meet.
