I've seen our stance on partial answers (where some, but not all, of the puzzle is solved), and I agree with our philosophy that they're basically a good thing for this site. How far, though, does this stretch?
Could a valid partial answer make no actual progress against the puzzle, but still be acceptable and useful? This, for example, could take the form of listing a few complex or difficult things that the solver has tried, but wind up not working.
Though this isn't tied to any specific question or type of question, it was the "What is a Word" puzzles that got this question into my head. For some of these puzzles, I tend to write bits of code to perform various mutations to the words. On this unanswered puzzle, my code has applied ROT-N to various letters in various ways. I feel that this could be useful, to spark ideas in other puzzlers, or to provide/prompt feedback to/from OP. Additionally, it would let OP know that people are indeed interested in their puzzle.
However, this type of answer wouldn't actually make real progress toward the solution, since there generally should be significantly more wrong approaches than right ones.
Even if these answers are permissible, we certainly need some quality threshold (voting is the primary mechanism for this already). Answers that list easy or obvious things like "They all don't start with the same letter, so that's not it" aren't very useful to anyone, but answers that rule out looking at the parity of the ascii codes might be useful to some solvers.
So, do we think that answers that rule out approaches (and do little else) are valid and useful partial answers, or should they be avoided for being not-so-helpful clutter?