Why monitor bytes sent and received on mysql
First, let's identify each status variable:


Bytes_received: The number of bytes received from all clients.
Byte_sent: The number of bytes sent to all clients.


The only place I can think of where these number would make sense would be in the network. These status values represent the amount of data passing in and out of DB Connections. These bytes would most likely be visible from another perspective: the Operating System.

You could measure the amount on incoming/outgoing traffic in netstat against MySQL's view of it. If the amount of incoming data is low, or if the amount of outgoing data from MySQL is significantly higher than netstat says, check MySQL and/or the network. You may also want to look for any signs of dropped packets along any interfaces.

In light of this, when it comes to tuning, the only thing I can think of that you may want to tune is setting two things:


net_buffer_length : Connection and result buffer size
max_allowed_packet : Maximum packet size used internally by MySQL 


What is a MySQL Packet ?

According to the page 99 of the Book



here are paragraphs 1-3 explaining it:


  MySQL network communication code was
  written under the assumption that
  queries are always reasonably short,
  and therefore can be sent to and
  processed by the server in one chunk,
  which is called a packet in MySQL
  terminology. The server allocates the
  memory for a temporary buffer to store
  the packet, and it requests enough to
  fit it entirely. This architecture
  requires a precaution to avoid having
  the server run out of memory---a cap
  on the size of the packet, which this
  option accomplishes.
  
  The code of interest in relation to
  this option is found in
  sql/net_serv.cc. Take a look at my_net_read(), then follow the call to my_real_read() and pay
  particular attention to
  net_realloc().
  
  This variable also limits the length
  of a result of many string functons.
  See sql/field.cc and
  sql/intem_strfunc.cc for details.


Given this information, you may want to


raise net_buffer_length to its max value of 1048576
raise max_allowed_packet to 256M, 512M, or 1G (especially if you have BLOB data)