TF-IDF for long documents is in general not very informative. TF-IDF works well for shorter documents that are largely about one topic. It will most likely no

TF-IDF for long documents is in general not very informative. TF-IDF works well for shorter documents that are largely about one topic. It will most likely not catch onto the fact that the Iliad is about the Trojan war. (TF-IDF vectors are largely viewed as a cute trick but ultimately a bit of a dead end in classic information retrieval.) That said, cosine similarity is definitely still useful for large vectors of things that aside from tf-idf.