Apparently it gets a mention in Lado’s 1957 classic Linguistics Across Cultures and I once came across someone trying to prove something fundamental by teaching Japanese students these sounds.
It’s true that in Japanese they rely only on length to distinguish between the two most similar vowels to “ship” and “sheep” whereas in English the mouth position is also different. However, in eight years of daily conversations in all kinds of levels of English in Japan I can’t remember a single incident of those sounds causing miscommunication in either direction, whereas it was every day or even every lesson in Spain, where there is no short vowel/ long vowel distinction at all.
I know nowadays it is fashionable to argue that the length differences in English vowels are unimportant or even absent in some circumstances (just as it is fashionable to argue that voiced/ unvoiced is a useless or even false distinction), but my experiences of communicating and teaching suggest otherwise. It can help Spanish students to concentrate on the wider spread mouth of “cheap” and “sleep”, given the problems they have with vowel length, but even one second of class time spent on this in Japan is completely wasted. To the authors of that pointless study – try teaching Japanese consonant clusters instead, will you?