Original: The enharmonic equivalent B-flat minor is often used in most musical compositions instead of A-sharp minor, thus indicating that A-sharp minor is not a practical key for compositions and is one of the least used minor keys in music.
Simplified: A-sharp minor has the enharmonic equivalent of B-flat minor. This is often used in most musical compositions instead of A-sharp minor, because A-sharp minor is not a useful key for compositions and is one of the least used minor keys in music.