Consider the idiomatic way of interating backward through a array:

  for(i=n; i-- > 0 ;)
    { /* operate on a[i] */ }

converting i--; to a statement at the start of block makes it less clear that it's part of the iteration idiom rather than a ad hoc adjustment that's specific to this particular logic. There are other examples, but they're either more involved or statementification is less obviously wrong.