MP3 bitrate controls the balance between file size and sound quality. A higher bitrate usually produces better sound, but it also creates a larger file.
64 kbps can be acceptable for simple speech clips where file size matters more than quality. It is not ideal for music because it can sound compressed.
128 kbps is a common everyday choice for small clips and general web use. It keeps file size manageable while maintaining acceptable quality for many purposes.
192 kbps is a stronger option when you want better quality without making the file as large as 320 kbps.
320 kbps is the highest common MP3 bitrate and is useful when quality matters most. It is still lossy, but it preserves more detail than lower bitrate exports.