I believe that bonsai should not always be manicured to show quality. They need occasional grow out to restore energy and vigour so I intentionally let my trees get a bit shaggy occasionally.
Note that not trimming can put trees under stress in hot weather. Less leaves and shoots means the tree can manage with less water so trimming can be a good strategy in hot weather.
Conversely removing too much foliage in hot weather can suddenly expose the trunk to strong sun and cause sunburn of the bark.