The importance of Summer Pruning of Bonsai

 There are many reasons to prune most deciduous bonsai in Summer.

Firstly, a heavy pruning in summer reduces the 'transpiration load' on most broadleaf deciduous bonsai.  This reduces water stress.

The resultant 'Summer flush' of this pruning is Important to the design and development of deciduous bonsai.  If you get the timing right this late flush can produce smaller leaves and finer branching; increasing branch ramification.