句尾现在分词短语的作用

下面是《英语语法大全》英文版P1126上的一部分内容，作者的有些叙述不好理解，我简化一下，只针对作者所举的含有句尾现在分词短语的例句，来说说我的理解，大家看对不对。

In spite of their resemblance to nonrestrictive relative clauses, supplementive clauses need not be separated from their matrix clause intonationally when they occur in final position. The following are therefore alternative renderings of the same sentence, differing only in that [1] has two focuses of information, whereas [2] has only one:

The manager apPROCHED us, SMILING. [1]

The manager approached us SMILING. [2]

One result of the alternative shown in [2] is the possible neutralization of the formal difference between nonfinite clauses functioning as supplementive clauses and those functioning as complementation of the verb. Thus [3] is ambiguous:

I saw Pam going home. [3]

On one interpretation (that of the supplementive clause), ‘I’ is the implied subject of ‘going home’, whereas on the other (that of verb complementation), ‘Pam’ is the overt subject. 

Another result of the lack of intonation is illustrated in [4] and [5]. When the -ing participant immediately follows certain finite verbs with existential meaning, the latter seem close to being aspectual catenatives:

Frank sat reading the newspaper. [4]

Edith came running towards us. [5]

Further, a sentence such as [6] is ambiguous in more than one way: 

I caught the boy waiting for my daughter. [6]

In addition to the two possible structures of [3, this may be interpreted as having a third structure, in which the nonfinite clause is a postmodifying clause: 

‘I caught the boy while I was waiting for my daughter.’ [supplementive clause. 

‘I caught the boy in the act of waiting for my daughter.’ [verb complementation] 

‘I caught the boy who was waiting for my daughter.’ [postmodification] 

我的理解：

The manager apPROCHED us, SMILING. [1]

The manager approached us SMILING. [2]

举这两个例子，作者想说，有的时候，位于句尾的现在分词短语前有没有停顿（书面加不加逗号）都一样，即[1]和[2]意思一样，现在分词短语都是增补性分句（即作状语），两者唯一的区别是：[1]有两个信息焦点，[2]有一个。

I saw Pam going home. [3]

针对这个例子，作者想说，类似[3]这样的句子，有没有停顿（逗号）意义就有不同了，会有两种解读：第一种，“I”是“going home”的隐含主语，也就是说现在分词短语going home是增补分句（即作状语）；第二种，“Pam”是“going home”的显性主语，即现在分词短语going home是动词补足语。如果going home前有了停顿（逗号），则只有一种含义：going home是增补分句（即作状语）。

Frank sat reading the newspaper. [4]

Edith came running towards us. [5]

作者举这两个例子，又想说明，有的句子（谓语动词为存在动词），句尾现在分词短语前没有停顿（逗号）话，会让人感觉这是链接动词的用法，即类似I like eating fish.的用法。

I caught the boy waiting for my daughter. [6]

作者举这个例子，又想说明，有的句子，句尾分词短语前没有停顿（逗号）的话，分词短语的作用除了可作上面的提到的其中两种解读之外，还可以有第三种解读，即后置定语。

我不敢质疑大师，应该是我水平不够，我怎么感觉英文版的有些叙述特别绕，因而意思上不是特别清晰。

请各位老师不吝赐教！