I think what DCNH may be useful for is for thinking about why someone (dual or not) might not be good for you. Let's say you're seeing someone and you're not sure if it feels quite right. Let's use me as an example (I'm a H). If I was dating someone and they seemed a bit too D-ish or H-ish, well maybe it's a sign that it's not the right person for you. If they seem C-ish or a C/N-ish then, it's a sign that it might have actual potential. This stuff can often be instinctive but it's not always- you might need to consider the options. Also, you might like the person (and they are a matching subtype)- C for me, but it's not working and maybe you need to think about why..well maybe this person is mostly C but with a strong dash of D. And therefore not the 'right' C for you