perldoc perlstyle:

Learn it, live it, love it. You never know when I’m going to be cleaning up your mess.

When in doubt, parenthesize. At the very least it will let some poor schmuck bounce on the % key in vi.
Even if you aren’t in doubt, consider the mental welfare of the person who has to maintain the code after you, and who will probably put parentheses in the wrong place.
–Larry Wall

Original