Taint checking?

citromatik has asked for the wisdom of the Perl Monks concerning the following question:

Hi,

I have encountered the following in production code:

if((defined ($command_str)) && ($command_str =~ /^(.*)$/)) {#taint che
+cking
 $command_str = $1;
 # blah, blah
[download]

Does this make any sense? is there any benefit in reassigning $command_str this way?

Thanks in advance

citromatik