Like toolic, I work on the principle of "when in doubt, parenthesize." I've also dealt with optimizing compilers that would handle something like

do i = 1, 10
   do j = 1, 10
      do k = 1, 10
          l = i + j + k
      enddo
   enddo
enddo
[download]

differently from

do i = 1, 10
   do j = 1, 10
      do k = 1, 10
          l = (i + j) + k
      enddo
   enddo
enddo
[download]

in that it would not recognize i + j as constant in the innermost loop in the first fragment, but would in the second. There are also cases where I've needed to force a specific order of operations to preclude under or overflow.

I also won't rule out the possibility that, unlike the compiler, I can get confused about logical tests that have multiple and's, or's, and not's; using (perhaps superfluous) parentheses will reduce my confusion.