Equated with the sign Scorpio, the 8th house covers a lot of ground: sex, death, intimacy, shared resources (partner funds, taxes, debts), inheritances, occult matters/astrology, and who you attract. When Saturn enters H8, you may suffer a crisis or loss in any of these areas. Debt issues that have been building come to a head, or you could find out you contracted an STD, for example. Saturn crises aren’t out of the blue, rather the result of something you’ve been sweeping under the rug.
Saturn in Sagittarius is the crystallization of options: Sag likes to expand, and Saturn focuses how to do it in a realistic manner. This transit will focus society on spirituality, religion, education, science, and how our beliefs about the universe may be incorrect/require broadening our minds as a culture. For you personally, these themes may be brought up via a near-death experience, education costs requiring loans, ending a restrictive intimate relationship to liberate yourself, etc.
If Saturn is passing through your 8th house, you either have Scorpio or Sagittarius on the cusp. A Scorpio-cusper (like myself) will intensely research, and attempt to gain control over, all the aforementioned H8 areas. We are also rather private and secretive about these items, and can attempt to mastermind in an effort to retain power. Because of the fixed nature we have around H8 themes, a Saturn transit can be tough because they put us in survival-mode. But Saturn in Sagittarius lightens the mood, and allows us to embrace change more easily.
A Sag-cusper feels open, light-hearted, adventurous, and possibly even exhibitionist about H8 matters, and may prefer intimacy with those from foreign cultures. These are the type to see sex as “no big deal,” perhaps as something to play at rather than take seriously, and therefore may break a few hearts in their inability to commit to one person! A Saturn transit for you may force you to choose one or two realistic options, rather than flit around in your normal fashion. You may also have to deal with paying back educational loans and other debts you’ve put off, at this time.