Yes, it is acceptable. Some people use it when they write Perl files that are both modules (they cay be used/required, they declare a namespace (package), they possibly export subroutines) and ordinary perl programs (they do useful work when run via perl file.pm). At the end of the file there is usually a line:

main unless caller;
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which checks whether the file is called as a module and runs the "main" sub if not.