SQL server 2008R2 default encryption?
SQL Server communicates using TDS, or Tabular Data Stream, protocol.  By default, TDS is not encrypted.

Encryption can be negotiated between the client and the server at time of connection.  Essentially, you enable encryption at the server, then roll it out by making the necessary changes at the client end.  Since encryption is not forced at this point you are simply reducing the visibility of some data over the wire.  Security is about layers of protection; encrypting communications, even if only some communication, is still a valuable layer in the security stack.

Once you have all clients configured to use TDS encryption, you configure the server to only accept encrypted connections.  At that point, all communication between the server and its clients will be encrypted.