这个句子中，that引导的就是表语从句，可以被省略，在表语从句中，这个that不充当句子成份，去掉也不会影响理解。so that结构，引导状语从句如此，以至于的意思.前面已经有了so了，后面就不能在用so了。
关于代词that和which的用法区别：
在定语从句中，当先行词是指物时，关系代词which可以由that代替，如果which不在介词之后，也可省略。在日常用语或口语中，which不作主语时可以省略。例：
Did you take away the book(which/that）I showed you yesterday?
你把我昨天给你看的那本书拿走了吗？
The hotel at which we stayed was both cheap and comfortable.
我们住的那家旅馆既便宜又舒适。
This is certainly not the book for which I paid./This is certainly not the book I paid for.
这肯定不是我付钱买的那本书。
但两者之间还有一定的区别，必须予以足够的重视。
一.that仅用在限制性定语从句中，通常不用逗号隔开，作宾语或介词宾语时，that 可以省去。例：
The letter that came this morning is from my father.
今晨收到的那封信是我父亲寄来的。
The watch(that)you gave me keeps perfect time.
你给我的那块手表走得准极了。
The photographs(that) you're looking at were taken by my brother.
你正看的这些相片是我弟弟照的。
二.which既可用在限制性定语从句中，作宾语或介词宾语时，which可以省去，也可用在非限制性定语从句中。例：
Did you see the letter that/which came today?
今天来的信你看到了没有？
This is the one of which I'm speaking./This is the one I'm speaking of.
这就是我说的那一个。
He changed his mind, which made me angry.
他改变了主意，使我很生气。
He admires Mrs.Brown, which surprises me.
他钦佩布郎太太，这使我感到惊奇。
根据句意和句子结构，不难判断出句中的 that 是多余的。
此句是一个标准的主谓双宾语结构，主语是 Ren's staunch dedication to service，谓语是 gave，后面是双宾语，即 sb = them，sth = an edge over their competitors（即 give sb sth）。如果把 that 放入句中，它不能充当任何成分，纯属多余。
基本句意是：Ren对服务的坚定奉献，给他们带来了与竞争对手相比而言的优势。
