“对于”can be replaced by“对”, while “对” has multiple meaning and can't be repaced by"对于" in all cases.

In different sentence has different meanings. Sometimes could be the same. Same: 对于我来说，你是最好的。you are the best for/to me. 对于=for/to 对我来说，你是最好的。 Different: 她对我笑。(correct ) 她对于我笑。(wrong)

举几个常用的例子吧： 我对他没兴趣。 I am not interested in him. 对与错并不重要。Right or wrong is not important. 她对我笑了笑。She smiled to me. 我对他很生气。I'm angry at him. 这对/对于我来说是个好机会。It's a good opportunity for me. 对/对于这个问题，你怎么看？What's your opinion about this question?