On some platforms select for timeouts won't work, so you have to use sleep instead.

$|++;
for (split //, "Just a proud\b\b\b\b\b\bnother Perl hacker,\n") {
  print;
  select (undef, undef, undef, 0.3);
}
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Without $|++ this would most emphatically not have the same effect. :-)

More practically, I have seen CGIs that use system calls fail if the CGI script was buffered, and the thing called did not use buffering. But most of the time you want buffering since it is easier on the system and makes IO faster.

UPDATE
Apparently by default Windows turns buffering off on interactive scripts. You may need to pipe the output of the above through the following script to see the effect of $|:

$| = 1;
while (read(STDIN, $buf, 1)) {
  print $buf;
}
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UPDATE 2
I have been informed that this doesn't work. I know I have gotten the principle working on NT before, but without Windows to test on, I can't really debug this one. Sorry.