a)	To help prevent limb shedding
b)	To alleviate obstruction – i.e.
1.	Road/footpath clearance (crown lift)
2.	Clear power and other service lines
3.	Visibility splays and highway sign obstruction, including over waterways
4.	Create more light to windows
5.	Clear house roof and gutterings
6.	Re-shape and balance crown for aesthetic purposes
7.	To allow a more desirable species to develop and finally replace the tree being worked on.  This can be 
        important when a nurse crop has been planted as a short term measure.

The nurse crop induces terminal growth and discourages heavy side limbs developing due to shading them to the extent that lack of light stops the process of photosynthesis. It is always preferable to use this natural method of producing a specimen long term tree with a long straight stem and balanced crown form, as fungal and bacterial diseases often enter through pruning wounds.

Fungal diseases can remain in a latent state for many years then triggered into parasitic activity by stress:

Stress may be due to many factors, drought, ground compaction, prolonged freezing, root severance, e.g. trenches or cultivation’s over the root zone. These are just a few non-living agents which would cause stress in a tree. The living agents include insect attack, mammals, fungi, bacteria, virus and above all, human vandalism.