Benzodiazepines themselves are pretty physiologically hard to overdose on especially if you have some tolerance, you need to take quite a large amount. Alcohol however it's a lot easier to have a dangerous and possibly fatal overdose.
The risk with mixing the two comes not so much from say taking a lot of benzos and only a small amount of benzos - mostly it's that benzos themselves lower the threshold needed to be crossed in your drinking before you reach negative consequences like alcohol poisoning.
Any benzo/alcohol combo in any amount (unless you have existing tolerances and keep the amounts low) can be dangerous in other ways, like a complete lack of inhibitions where you do crazy shit like trying to drive and getting in accidents, or just generally doing stupid shit, think some of the crazy Ambien stories you've read, a lot of that applies to blackout doses of Benzos or Benzos combined with other GABAergics.
I think the dangers of the combo are often overstated and people like to make out like any amount of any benzo in combination with even the smallest amounts of alcohol is asking for a death wish - this is plain true, but as a result of people discovering this is the case, they forget that there are serious risks when such a combo is not carried out correctly.
For example drinking yourself shit-faced and then consuming just a small amount of benzos could lead you to undergo alcohol poisoning. Also a very large amount of benzos with lower amounts of alcohol can also be risky, but in general it's worse to consume a large amount of alcohol with a small amount of benzos than it is to do the reverse.
When combining the two (bear in mind I have tolerance, if you don't then you should practise a lot more cautiously) I've found it's best to do a few things:
1) Set your limits for both alcohol and benzos before the night begins, make sure any extra benzos and alcohol are out of your reach and not there to be consumed, it's very common when taking benzos or drinking alcohol or using any GABAergic in general that you end up taking more and more due to amnesia (forgetting you've taken doses) or due to relaxed inhibitions making you say "fuck it I can handle more" when you might already be in dangerous territory as is, especially if you've forgotten the true amounts you've consumed.
2) Good limits for benzos are low-average dose of the benzo in question, so you're in no danger of blacking out or doing stupid shit when you add the alcohol. Then the alcohol the amount you normally need to get tipsy but not fully drunk usually works well, the compounding effects you'll feel drunk rather than just tipsy, and the benzo feel will be potentiated nicely.
3) Don't throw other depressants into the mix, occasionally those addicted or with a previous addiction to a substance know their limits and mix as much as Benzos + Opiates + a whole rather of other CNS depressants and understand just how low the doses need to be in such mixes to do it safely but it's playing with fire and unless you have years of previous use with all compounds under your belt, quite a tolerance, and know your limits it's to be avoided at all costs as it has killed many many people.
For example if 2 beers gets you tipsy, 4 beers gets you drunk, and 1mg Xanax is a good dose for you, 1mg Xanax + 2 beers should be good, you'll still get drunk from such a combo like if you had your normal 4 beers, get to enjoy the Xanax feeling too, and not have to worry about being at overdose risk.
The safest way to do it too is to stagger your doses and start small, so start with maybe 0.5mg Xanax and start drinking your first beer slowly to see how strong the feeling is at that level, if you find it way too weak then take the other 0.5mg Xanax, wait for it to hit fully and then slowly sip through your second beer. Or alternatively take the 1mg Xanax right away and then just drink your beers really slowly, when you start feeling the slightest bit drunk and/or start forgetting things/wanting to do crazy shit etc it's time to stop taking any more for sure
That said everyone is different and combining CNS depressants isn't something advisable, I'd be a hypocrite though telling you not to do it as it's something I do, but I've done it for years and it took me a lot of failures where I nearly put my life at risk (and even ODed a couple of times) to work out my own safe limits, so always start very small and remember these substances potentiate each other.
