In February 2017, United Airlines introduced their new Basic Economy fares on selected routes. The Basic Economy fares will save you money but you will have to give up some basic comforts in exchange.
Here is the difference between Basic Economy and Standard Economy
Basic Economy Standard Economy
Choose, change or upgrade seats No Yes
Sit with you group or family No Yes
Travel with a full size carry-on No Yes
Change your flight No Yes
MileagePlus Premier qualifying No Yes
credit & lifetime miles
Passengers choosing Basic Economy will not be able to choose their seats at the time of booking. Instead they will be give their seat assignment upon check-in. They also can not make any changes to their seat assignments or upgrade their seats. There is a high chance you will not be sitting with your travel companions. You will most likely be given the middle seats that nobody wants and be spread throughout the plane.
Passengers also will be limited to one person item such as a purse or computer bag which must fit underneath your seat. You will not be able to put anything in the overhead bins. MiliagePlus members will not receive their usual travel benefits.
So passengers will have to weigh the saving of Basic Economy and the conveniences of Standard Economy to determine which fare is best for them.