Omitting parens around argument lists has issues. You've already mentioned the problem with omitting parens in conjunction with || instead of or. There's also

print (3+4)*5;  # Prints 7
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At least that one warns.

>perl -we"print (3+4)*5"
print (...) interpreted as function at -e line 1.
Useless use of multiplication (*) in void context at -e line 1.
7
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