In News From A Near Future: Airlines discover (by means of queueing theory, modelling and big data analysis) that if they pay you a small fee -- in the form of

In News From A Near Future: Airlines discover (by means of queueing theory, modelling and big data analysis) that if they pay you a small fee -- in the form of a tiny discount on your ticket (a few dollars) -- for putting your luggage in the cargo hold instead of taking it on-board with you, they save tons of money because planes get to load/unload faster, so reducing their time at the gate, essentially trading their gate-time for your baggage-claim time, so increasing profitability. Seriously, these fads come and go like the order that shelves are stocked in supermarkets. It's all just a fashion industry and frequently only the thinnest of actual data/logic to back up some accountant/marketer's assertions that it is so. Watch in a few years' time when the fashion reverses...