Where not to use IDF?

Question

What are the cases when the frequency of the reverse document is not useful when searching for information?

Answer 1

You may not want to use IDF if you do not want to weigh rare terms more on your system than common terms. Moreover, calculating idf is an expensive operation. This is evident from the fact that in the most commonly used calculation scheme ie lnc.ltc, we do not calculate idf estimates for the terms used in the document.

Also, if your search engine processes only one query word, using idf is useless, as if it were the same for each document. Hope this helps.