Divers go in the spa so they don't get cold after each dive.
to col off
Mainly because the pool is cold and the hot tub keeps them warm and loose instead of cold and stiff. Also allows them to focus for the next dive.
because the water is so cold from a high dive they go in the wading pool to warm back up
the waves/ripples created by divers are dispersed more evenly in a larger pool vs. a smaller pool which makes splash from the actual dive and ricochet from the sides more difficult to differentiate
they go as deep as the bottom of the pool
You usually see them in diving competitions. The water spouting into the pool gives the divers perspective on the distance to the surface of the pool.
They sit in warm water after they dive because the pool water is cold and they want to keep their muscles warm and ready to twist and turn again for their next dive.
Aside from staying in a routine if you watch some of the female divers, they leave the diving pool covering their breasts to prevent showing their nipples which harden in the diving pool. They will recheck their look after warming themselves in the hot tub.-