Let's be honest, Bioweapon Defense Mode on the Tesla Model S and Model X bears a silly name, but it's some serious tech with potentially serious health benefits. The system takes outside air, puts it through a HEPA filtration system, and pressurizes the interior cabin to prevent the outside from leaking in. There's been some kerfuffle about whether or not it's a "true" bioweapon defense, so Tesla decided to put it to the test: they built an airtight bubble, put a Model X and their engineers inside, and filled the entire space with "extreme levels of pollution".
Here's how Tesla describes the test:
We then decided to take things a step further and test the complete system as we would on the road, but in an environment where we could precisely control and carefully monitor atmospheric conditions. A Model X was placed in a large bubble contaminated with extreme levels of pollution (1,000 µg/m3 of PM2.5 vs. the EPA's "good" air quality index limit of 12 µg/m3). We then closed the falcon doors and activated Bioweapon Defense Mode.
The plot below shows the subsequent evolution in pollution levels inside the vehicle and inside the bubble. In less than two minutes, the HEPA filtration system had scrubbed the air in Model X, bringing pollution levels from an extremely dangerous 1,000 µg/m3 to levels so low as to be undetectable (below the noise floor) by our instruments, allowing us to remove our gas masks and breathe fresh air while sitting inside a bubble of pollution.
Not only did the vehicle system completely scrub the cabin air, but in the ensuing minutes, it began to vacuum the air outside the car as well, reducing PM2.5 levels by 40%. In other words, Bioweapon Defense Mode is not a marketing statement, it is real. You can literally survive a military grade bio attack by sitting in your car.
Which is to say that it's an incredibly impressive system, though the chances of your being able to use it to survive an actual bioweapon attack are relatively low — biological attacks use viruses that are slip-through-HEPA-filters-small and typically act on long enough of a scale that you wouldn't know that you'd need to activate the filters until it was already too late. That said... if you happen to know that you're entering an airborne biohazard area with your Tesla (why are you doing this?), Bioweapon Defense Mode could be of use.
More practically, however, it'll be of far greater use in everyday driving, be it a smog-congested rush hour highway or a freshly fertilized pasture in the countryside, Bioweapon Defense Mode pledges to filter it all out. Bioweapon Defense Mode is an option on both the Model S and Model X as part of the Premium Upgrades Package.