SQL Guide : Tuning performance with SQL : Tuning SQL statements and applications : Using stored procedure language
  
Using stored procedure language
Using stored procedures can speed up some operations in two ways:
Statements in stored procedures are parsed and compiled once and then stored in compiled form. Statements outside stored procedures are re-parsed and compiled every time that they are executed. Thus, putting statements in stored procedures reduces overhead (parsing and compiling) if the statements are executed more than once.
If you have multiple statements inside a single stored procedure, calling that stored procedure once may use fewer network “trips” than passing each statement individually from the client to the server.
See also
Tuning SQL statements and applications