The first comment is really the basis of the issue. sprintf will let you store off the results into a variable for later use, while printf will simply wrap the results and send them to STDOUT (or the CGI page).

For example:

# Using printf
printf( "%100s\n", 'This will just print to STDOUT; will not return ot
+herwise.' );

# Using sprintf
my $var = sprintf( "%100s\n", 'This will be stored off to $var, where 
+I will use it later' );
print_var( $var );

sub print_var {
  my ( $data ) = @_;
  print $data;
}
[download]

This specific example will really, effectively, do the same thing. Although it can sometimes be nice to use the formatted result of sprintf in other areas of a given application.

Hope this helps, and good luck!