Hello, ashdan!
To say that a horary chart is not radical is the same of saying that the chart is invalid and should not be used to answer the question. This may be due to a lot of "problems", the question is asked too early, or too late, the astrologer does not have what it takes to answer, or this is not a good time to ask, etc.
Now I will tell you something that my experience showed me, but it is not something in the books. As you said, many times charts that are not radical do yield very good and precise answers. This is so strong and common that I, personally, rarely am worried with signs of non radical charts. I do take notice of these, but I read the chart anyway. Remember this is my personal experience, and not necessarily something that others astrologers will agree.