Unless you're aware, stay very far away.
As a travel professional, I often read about how razor-thin airlines' margins are. These companies live in a fiercely competitive, commoditized sector, where consumers are constantly exposed to discounted fares from airlines and OTAs alike. I can't blame them for attempting to differentiate by way of "status reveal" programs like Delta's, which boards passengers in small, ticket price-based groups rather than the cattle calls of the past. It costs them nothing to implement, and their data suggests that travelers prefer boarding in smaller numbers at a time - a contrast to most airlines' cattle calls.
But this extraordinary competition has also given birth to a particularly dreadful low-priced product: the Basic Economy ticket. To fly at the lower seat price, checked bag fees always apply. But worse, the traveler cannot secure a seat assignment at the time of purchase; the airline makes that decision for them, hours before the flight. And until late last summer, American Airlines didn't even allow Basic Economy ticket holders to bring carry-on bags.
What is frustrating about these fares is that it can be very difficult for travelers to distinguish Basic Economy tickets from typical coach seats, until it's too late. This is even true for those of us who book flights for a living, because many online vendors identify the fares as "coach", until the restrictions and limitations are made it clear in the fine print two clicks away.
Some airlines' nickel-and-dime business model puts them firmly on travelers' "never ever" list. But the emergence of Basic Economy isn't specific to one or two carriers, it's ubiquitous. And sadly, it appears to be here to stay... unless a single traveler is packing light and flying a short distance, that low price hook will always find enough unsuspecting fish to bite.