我认为没有什么大的区别,就是一个是表语从句,一个是状语从句
比如：That is because I love her.
（为什么我...,因为我爱她）
I'm late,because I got up late.
如果非要有区别,有这样一点：
状语从句可以用动词分词形式直接表示,表语从句当然就不行了,Eg:
He doesn't want to go there because he knows there's a war right now.
改成：Knowing there's a war right now,he doesn't want to go there.