if you're in a burning or depressurizing vehicle, as happened to Mir, or if you're very sick or injured. When Mir had it's fire several years ago, the crew was very close to doing an emergency evacuation.

We used to hear how the old Soviet Union didn't put much value on human life. That was certainly true for ordinary soldiers (and appears to still be true today), but even at the height of the Cold War, the Soviets always provided an escape spacecraft for their space station crews.* We did the same for Skylab. Whether it needs to be a full spacecraft or a more radical idea like MOOSE, there does need to be a way to keep the crew alive, preferably through a reentry, but at least in a protected area of last resort.

* The Russians also make some very good ejection seats, plus they have a proven escape system on their Soyuz spacecraft.