The SAP in a tree is like the blood in our bodies.
The tree SAP transports the trees vital minerals, nutrients and the sugar to all parts of the tree.
Without the tree sap in the tree the tree could not survive.
Trees are living things and need the tree sap to get those minerals and nutrients as well as sugar through the tree.
If the tree lost all it's tree sap then the tree would die.
So the tree sap is vital to the tree to live.
Just like the tree needs it's roots to suck up water so that it can survive.