To allow more light or water to reach the ground.

To remove dead, dying or dangerous branches.

 To reduce length or weight whilst maintaining the flowing lines of the tree.

To reduce the crown size in all directions to leave a balanced crown structure. It is a complete crown treatment and not just a reduction in height without dealing with side branches. It is normally specified as a percentage and refers to the branch proportion to be removed in relation to the total branch length from tip to trunk.

To improve access and clearance. All of these operations require care and skill to be done well The results of hurried or over-zealous pruning can disfigure a tree for ever Heavy crown reduction; removing too much of the crown.