Upfront, I want to acknowledge that benzos are highly addictive, shouldn't be used long-term, and their use by people with personality disorders is risky because of our propensity for impulsivity and self-harm. There's a high potential to abuse the medication intentionally or become addicted to it.  

That said, I was prescribed a very short course of Valium recently for acute anxiety (not really BPD related), and it calmed me down. It defused my anxiety and aggression - it 'tranquillised my mind', to quote the Rolling Stones song. I found this positive, because:

a) It gave me a bit of time to adjust to the upsetting events. When something upsetting happens, the worst time is immediately afterwards. No matter the event, time gives perspective.

b) When I'm distressed, it can often feel like contacting the person and trying to elicit a desired response or explanation is the only way to relieve my anxiety. Now, I had a decent alternative. I've tried mindfulness, distraction, the gym, DBT; because I have two anxiety disorders, including OCD, they're not always super effective. I'll go to the gym or do mindfulness, but still be overwhelmed by anxiety and desire to make contact when it's over. However, my mind can't overpower medication slowing it down.  So the knowledge that I had an effective way to relieve tension/anxiety completely independent from contacting the person was a relief. 

I can't help but think that if I'd known about benzodiazepines earlier, various negative events might have been avoided. I'm the type of BPD who is 'normal' for months, then can overreact in the context of (for example) a relationship break-up. If I'd known I had a legitimate means of anxiety relief, perhaps a) that knowledge alone would have calmed me down, and b) the medication itself may have given me space to adjust to the event without freaking out.

Not really sure where I'm going with this - what have your experiences been?

(Also, again, I want to reiterate that benzos probably aren't great for a lot of people. I dislike sedatives and drugs that impair my cognition, I rarely drink, and I'm well-versed in the negative long-term cognitive and physical effects of benzos, so I have no desire to take them on a regular basis. However, for people who prefer sedatives such as alcohol, the appeal of taking the medication daily for anxiety relief, or to misuse it for the same reason, might be quite strong.   Additionally, if you self-harm, they are dangerous because overdose can cause death. 

However, for a subset of anxious BPD people who otherwise dislike sedatives, they (in my initial impression) appear quite effective for short-term anxiety/BPD episode management.)