At one point in my life (not very long ago ;)), I had the temptation to create lots of little 2-line and 3-line functions (probably coming from an OO background in school, where I was taught to make even simple variable accesses into object methods...)

But, consider the following code:

# test1.pl (uses no user-defined functions):
for($i = 0; $i < 100000; $i++) {
        print $i;
}

# test2.pl (uses a simple function):
for($i = 0; $i < 100000; $i++) {
        print func($i);
}
sub func {
        return $_[0];
}

# OUTPUT
[falkkin@shadow ~/perl] time perl test1.pl > /dev/null

real    0m4.826s
user    0m4.240s
sys     0m0.010s
[falkkin@shadow ~/perl] time perl test2.pl > /dev/null

real    0m14.227s
user    0m14.100s
sys     0m0.050s

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It's clear in this case that the overhead involved in calling a function (mostly involving pushing variables to perl's stack and popping them back off) makes the code run roughly 3 times more slowly. Generally, I try to avoid calls to "small" functions in inner loops whenever performance is anything of an issue; if I'm only reusing those few lines of code once or twice in a program, it's just not worth it to create a function for it, in my opinion.