Crown raising, also known as “Crown Lifting”, is a process of raising the lower canopy of the tree up to a required height.  Whether this is a singular low-lying branch or the entire lower canopy, raising the lower canopies of trees gives much needed clearance from garden structures, such as sheds/garages/greenhouses. Larger trees can potentially damage buildings and rooftops if left unmaintained. 
 
Tress in public areas should be maintained by raising the lower canopies so pedestrian access is not impaired along footways, woodland tracks or other public areas.  Injuries may be caused which may leave the tree owner liable!  
 
Low canopy trees in garden areas once raised can make getting around the garden with the lawnmower easier, to preventing lower branches contacting with the ground that may cause damage to branch tips & budding area.    
 
To improve and increase light flow into the understory below, often carried out with crown thinning for maximum effect or, just to reshape the lower crown to alter aesthetical appearance.  
 
Good examples of low canopy trees are weeping willows & other weeping species, apples & other “Heavy Fruit” bearing trees can suffer from loss of crops when not managed.