Sometimes, for the sake of readability¹, assigning '' to a variable is better that leaving it undefined, or assigning undef.

That said, it is possible for assigning '' to a variable hides errors that might otherwise be detected by the warning.

As long as the coder is aware of the trade-offs, the coder can choose the alternative that best fits a given situation.

---

¹ Just adding a comment explaining what you are doing and why can actually confuse the reader:

my $buf; # leave value as undefined so use before a real value is avai
+lable will result in a warning message.
...;
while (<$input>) {
    ...;
    $buf .= $newletter; # not an error because appending to an undef v
+alue is treated the same as appending to an empty string
}
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While the above is certainly valid Perl code (and doesn't produce a warning), there are a lot of code reviewers who will reject this, citing it as being confusing.

And, often, the same reviewers will reject:

    if (defined $buf) { $buf .= $newletter; }
    else { $buf = $newletter; }
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as being too complex.

But:

my $buf = '';
...;
while (<$input>) { ...; $buf .= $newletter; }
[download]

is clear about what is being done and comfortable to the reviewers.

Sometimes debugging a weird bug is easier than arguing with the reviewers.