两者的区别是:介词后面连接的分别是somebody(人物)和something(事物)。be useful to通常在to后面加somebody,意思是对…有益;对…有用;表示对某人是有用。be useful for通常在for后面加something,意思是对…有作用;具有…用途,表示对某人来说做某事是有作用。
be useful to造句:This reference book is very useful to our study。这本参考书对我们的学习很有用。We all know trees are very useful to human。我们都知道树对人类很有用。The canal has proved useful to the county in many ways。这条运河在许多方面对这个县很有用。
be useful for造句:It is very useful for a person to know how to swim。对一个人来说,学会游泳是非常有用的。The book is useful for making sentences。这本书对造句很有用。I think it would be useful for you to learn the basics of marketing。我认为学习市场营销的基础知识对你很有用。