My Chevy Volt has a 15kwh pack, and only lets you use 10kwh. The bottom 2 and the top 2 are never accessible. Which means the batteries are never depleted, and never fully charged. I bought it knowing I have 10kwh to use around town or on trips (afterward the gas engine turns on). I use those 10kwh every single day, for all 177k miles of the cars life so far. I still get the same 10.3kwh I got on day one I made my purchase decision based on.
Tesla should advertise their packs the same way, explaining that the outlier 10kw are for emergencies too.