The body is the most obvious. I can always feel the difference between the stress that I hold in my body before the float and after I get out.
The mind is a little trickier. It takes a bit for it to calm down; for the voices to settle. I have to stay somewhat alert in order to release those though and to let them just float away. Occasionally I will let a thought that less troublesome run around in the darkness and let it take on its trip with it. Received clarity and vision from those instances.
But it is my heart, my spirit, that be befits the most from the floats. No pain, no suffering, just a moment of peace.