为什么“After having looked at his watch,he hurried to the stati

为什么“After having looked at his watch,he hurried to the station.”这个句子可用“After looking at his watch,he hurried to the station.”代替,而“After having spent whole mornings on the river,I always go home with an empty bag.”不能用“After spending whole mornings on the river,I always go home with an empty bag.”代替?动名词的完成形式何时可用一般形式代替,何时不能?