An astrologer asked the following in a discussion group: "Saturn in Capricorn, ruling the 10th and in the 10th. Is it a good placement ? Or a negative?"
That was it. That was the question. No context, no background. Nothing.
It can certainly be a malefic or a benefic; it is always relative to the chart. The chart, of course, is a symbol of the context being studied, be it a native, a country, an event, or any picture the querent’s mind creates when asking a horary.
In practice, there cannot be a benefic or malefic without a context. A planet without a context has meaning only in theory, or in the astrologer’s fertile imagination. Sadly, there is a prevalent habit among astrologers to jump into and use those terms without context; and not only beginners.
Suppose that our angular dignified Saturn in Capricorn is the significator of your executioner.
If your question was: will I die painlessly? That might mean that he has sharpened his blade and that he has a firm stroke and bears no negative feelings about his job. Is Saturn a malefic of benefic here? Now suppose you are signified by the Moon in this context; Saturn in Capricorn does not like you! Is Saturn a malefic of benefic now?

Other examples:
- Saturn in Capricorn could make for a nasty case of arthritis if it is the cause of your illness in horary or decumbiture.
- Jupiter in Cancer could show Pneumonia. The cause of the illness is ALWAYS malefic, no matter what planet it is or where it is.
- If our angular Saturn in Capricorn is the significator of your anti-virus software that would be wonderful: we want a dignified and accidentally strong immune system, be it for our bodies or our computers. Saturn is a benefic in this case.
Also, since good astrology is a reflection of real life rather than of some astrologer’s fantasies, it is worth noting that many things in life are not “either” benefic “or” malefic exclusively.
In many situations whatever is being inquired about is shown to be a bit of both. This is so clearly exemplified in relationship questions where two or more parties have contradictory feelings about one another. That is shown by receptions. What do you call a dignified Venus that does not want you to get near her? Benefic or Malefic?
I recommend caution and thoughtfulness when using the terms benefic and malefic and focus on context.
I have lost count of how many times I have seen astrologers get stuck in their interpretation of a chart due to adhering to those two terms when they do not apply to the context, or apply in a reversed way.
Another concept I hear to justify calling Mars and Saturn malefics is that they are “extreme”.
That is again nonsense if taken out of context. The “benefics” can be extreme too. Jupiter in Cancer is extremely expansive or watery or both. If you are expecting sunshine but get Jupiter in Cancer you will get a lot of rain. Malefic.
Venus in Pisces can be extremely sweet; if you have a tooth cavity or diabetes and you meet that Venus you are in trouble. Malefic.
If you have cancer (the illness) and Jupiter is near the cause of the illness cancer will grow. Malefic indeed.
All planets can work out in a positive or negative way according to the context. The fact that some contexts are more common than others does not justify making a definition and a rule that should be applied to every situation, which is exactly what many astrologers erroneously do. This is called “formatory thinking” in Gurdjieff’s terminology. A lot of it is found in traditional astrology.
It is understandable that we all want money and health and relationships to grow in size and/or quantity. Those contexts would call for Jupiter as a benefic, especially if dignified, and Saturn as a malefic.
Consider that most astrological inquiries are about things we want “more of” in life and that we want them easily; in those cases indeed, Saturn and Mars are a malefics and Jupiter and Venus would be benefics. So I believe those terms stuck with astrologers and then got into books in that fashion: due to that bias coming from the most common contexts in life, rather than from analysis.