Mostly it is useless, and it is potentially dangerous if you are used to C++ booleans. C++ has only one false value, so:

if (x == FALSE)
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will work every time. However, in Perl you have:

if ($x == $false)
if ($x eq $false)
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How do these work? What if $x = 0? or ''? or undef or 0.0? Are you sure? Perl has mutliple false values, so switching to a single false value is just asking for trouble.
Perl is perl, don't try to redefine the language. It is like the Pascal programmer who starts all his C code with:

#define BEGIN {
#define END }
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Server no purpose, confusing to others, and it just begging for weird ass bugs.