BSON (Binary JSON) is an extension of JSON, and was initially performed by Mongodb, a Nosql Document DB, which uses it to perform data storage.
By storing data on Mongodb, you are already using BSON.
In addition to all JSON data (null, String, Number, Array, Object), BSON supports:
1) Minkey, Maxkey, Timestamp - types used domestically in Mongodb;
2) Bindata - byte array for binary data;
3) Objectid - unique identifier of a Mongodb record;
4) Date - date representation;
5) Regular expressions.
All these extra attributes make data handling easier for CRUD (create, read, update and delete) data implementation for Mongodb.
BSON, as stated by the Bsonspec, is used by applications other than Mongodb.