be home和at home区别

be home 是系表结构，home只作表语，但at home 既可作表语，
也可以作定语、状语。
例如：
Who is home now? 也可以说成：Who is at home now?(作表语)
I usually do my work at home.(作状语)
Millions of visitors both at home and abroad come to
see the Great Wall every year.(作定语)

好像没什么区别，也不太清楚．