A bit is a single binary value. A bit is a single character stored in main memory. A bit is a collection of several bytes. A bit is a small unit of computer time. Binary devices are simple and easy to build.
Binary signals are unambiguous.
Binary devices are much faster than decimal devices. Patterns of bits can be used to represent anything symbolic. An analog signal has a discrete number of states. An analog signal is the only way that music can be recorded. An analog signal can never be converted into a binary signal.