Why do we have to submit tags to our discussions?

tags are use for classification and grouping. In any discussion, you will find below related discussion, that is where tag works.

i think it is usefull for people to find what are they looking for coz our discussion has been organized

This will facilitate in a search for a keyword,say,"submit","tags",'discussions",etc. You might have seen a search box,at the left hand side of the page. When one enters the words or topics,one wants to search for,in the search box,one can access many posts,comments etc which contain these words. BTW,there are 2 types of search boxes,namely,site search and web search.The first one will search this iste only and the one for web,will search the whole net.