在Web编程环境中，散列表与其他数据结构处理Key，Value对的用途是什么

I have heard of people using them for keeping track of session variables, but I really want to know if there are many uses for them and under what conditions it would be beneficial to employ a hashtable vs any other data structure that can handle key value pairs, like a dictionary for example.I have heard of people using them for keeping t