[lukefleed]

The other replies nailed it, but I'll add my two cents.

Vec<u8> may be the right call most of the time for most use cases. This library, however, is for when even 8 bits compared to 4 is too much. Another example, if all your values fit in 9 bits, you'd be forced to use Vec<u16> and waste 7 bits for every single number. With this structure, you just use 9 bits. That's almost a 2x space saving. At scale, that makes a difference.

For floats, you'd use fixed-point math, just like the other replies said. Your example of +/- 10.0 with 1e-6 precision would mean multiplying by 1,000,000 and storing the result as a 25-bit signed integer. When you read it back, you just divide. It's a decent saving over a 32-bit float.