When to use FastText?
The main principle behind fastText is that the morphological structure of a word carries important information about the meaning of the word, which is not taken into account by traditional word embeddings, which train a unique word embedding for every individual word. This is especially significant for morphologically rich languages (German, Turkish) in which a single word can have a large number of morphological forms, each of which might occur rarely, thus making it hard to train good word embeddings.
fastText attempts to solve this by treating each word as the aggregation of its subwords. For the sake of simplicity and language-independence, subwords are taken to be the character ngrams of the word. The vector for a word is simply taken to be the sum of all vectors of its component char-ngrams.
Training time for fastText is significantly higher than the Gensim version of Word2Vec (15min 42s vs 6min 42s on text8, 17 mil tokens, 5 epochs, and a vector size of 100).