I had a good conversation with a colleague yesterday about what you can expect from BJJ, especially as a smaller person (e.g., a 100 lb woman) facing a significantly larger assailant (e.g., a 200 lb man).
Stephan Kesting has written about 5 Most Important Self Defense Lessons from BJJ (article, podcast). I'll paraphrase them here, but the article includes much more detail and videos demonstrating each skill.
- Proximity Innoculation - avoiding panic and claustrophobia; minimize damage and maximize escape chances when your opponent has the top position
- Mount Escapes - self-defense variants from Full Mount and Side Mount
- Street Guard - an open guard for managing distance and minimizing damage when you are knocked down or fall down but your opponent remains standing
- Technical Stand-Up - standing up from a suppine/reclining position while minimizing the damage and danger from kicks/strikes
- Headlock Defense - escape technique that minimizes damage and pits your strongest muscles against your opponents arms
I'd add a few other things you'll get in a BJJ gym:
- How to Fall Down - minimize damage from being knocked down, taken down, or falling down, then land in a Bottom Position that minimizes your opponent's advantage
- Heirarchy of Positions - understanding the implications of the position you're in and having a couple well-practiced techniques for improving your position give you a huge advantage against someone who sorts grounded-grappling positions into the naive buckets of "top" and "bottom".
- Opposing Wills - physically imposing your will on another person, and having the same done to you is a useful and educational experience. Learning to do so without involving your emotions or ego can be challenging. (Sparring with a high level of intensity in boxing, wrestling, or any other martial art is just as good as BJJ in this respect, but you should get the experience somewhere.)
And one item that you may not find in your BJJ gym: closing the gap from striking range to standing clinch while minimizing risk.
If you look through these skills and compare it to the curriculum of Cecil Burch's Pugilism and Jiu-Jitsu seminars, or Craig Douglas' ECQC, you'll see they check almost all the boxes. Among Kesting, Burch, and Douglas, there seems to be a consensus that these are common, fundamental problems, and that BJJ has pretty good answers for them.
I train with weapons and advocate others do the same because even extraordinary unarmed skill guarantees nothing against a larger, stronger opponent, a better-trained one, an armed one, or one who brought friends – all assumptions we should make about real-world self-defense scenarios. That said, many self-defense "pop quizzes" turn out to only involve just one, unarmed, untrained assailant, who is substantially larger and/or stronger. In those cases, if you're unarmed, proficiency in the skills above give you as much advantage as anyone knows how to get at this point.