It doesn't "out weigh" everything, but it is important, especially for hatchlings. In a dry enviroment, hatchlings can actually become dehydrated over-night. When that happans on a consistant basis, the liver and kidneys slowly lose some of their abilty to filter and use what is needed by the body. So it's not the be all and end all, but it is part of the whole that keeps a tortoise growing well.
Danny