I think a deprivation tank in proper hands could be life-changing. The way I see it time space can be traveled. Well our present perceives the intervals between that  can be perceived at different rates and relative to the individual. Alone and isolated from outside stimuli the deprivation tank allows opportunity for an individual to change their rate. There is an infinity between the numbers 1 and 2 we rush to go from one second to the next but don't realize the Infinity that existed between the two. In a deprivation tank time can be taken advantage. A mind could live a lifetime in that brief time.  Sleep is probably even better place to take advantage of time.  A strong mental fortitude could grant you almost immortality.