Here’s what you’re giving up
Basic Economy is the same experience as your typical coach cabin -- soft drinks and snacks included, same sized seats, free reruns of Big Bang Theory -- just a lot more restricted. So you won’t be paying extra for that Biscoff cookie and the wisdom of Sheldon Cooper. But you also won’t be paying extra to pick your seat or carry on a bag, either, because you won’t be able to at all.
Though the Basic Economy fare rules differ from airline to airline (and always read them before you book), most allow only a small personal item to be carried on. None allows you the option to select your seat when you buy the ticket, and only American gives the option to do it at all, 48 hours before check-in, for a fee. All Basic Economy fares place you in the final boarding group, though again with American, elite members keep their priority boarding.