To clarify, using a lexical file handle is as follows:

my $handle;
open ($handle, $filename);
...
close ($handle);
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The advantage of lexicals is that you can use the same file handle (locally scoped) inside nested calls of a sub without collisions, and you can easily store the handle inside a data structure and retrieve it later.

Re: Three arguments for open vs two - is this really a major concern if you control all file paths yourself? Seems to me that you only really need to worry if the path contains user input, in which case tainting / parsing should do the trick. Can you explain how someone could do damage by accident rather than on purpose?