When I was a kid my dad had THE coolest bottle of booze on the planet. Actually it was two bottles, fused into a single decanter: Benedictine on one side, B&B (a blend of brandy and Benedictine) on the other, each with its own spout.
Coolest thing on earth to look at, but not once did I ever see it used.
Benedictine (technically “Bénédictine”) is an herbal liqueur composed of 27 plants and spices and brewed up by monks on and off since 1510; it’s bittersweet a lot like a typical amaro liqueur (like, say, Averna). Many likely find it not easy to drink on its own (though it’s used in tons of cocktail recipes), so they mixed it with cognac to create B&B.
The bottled version of B&B is arguably the world’s first pre-mixed cocktail, dating back to the 1930s. While both renditions are currently 80 proof (they were 86 proof until 1978), B&B is darker in color and somewhat less sweet, making it a bit more easygoing than straight Benedictine and easier to consume at room temperature, though both are quite a bit better served on the rocks. All told, B&B offers interesting citrus notes, with some vanilla, wood, and lots of complicated herbs here. Not at all bad as a digestif.
But frankly you can do better than B&B by taking straight Benedictine and mixing it half-and-half with your favorite cognac. I mixed Benedictine with Bache-Gabrielsen XO and there’s a lot more complexity here, and while I think the bitterness of the Benedictine ultimately detracts from the cognac’s more interesting characteristics, it’s really a personal preference issue of how you like your drink.
Bottom line: B&B is good, but you can probably improve on it with straight Benedictine and your favorite brandy without a whole lot more effort on your part.