My summation is that if it's an international flight and you're on UA metal 100%, then maybe for the cheap ticket as you lose being able to upgrade using miles or instruments and make free same-day changes. You get E+, lounge access, PQMs and regular luggage allowances. However, if it's international and you're going to have a portion of the iten on a partner airline, don't unless you're traveling with just a carryon or a single checked bag.
For domestic, Basic Economy doesn't make any sense for a status customer, since none of the stuff we hold dear such as PQMs, E+ for free and same day changes are available with the cheap fairs.