Cask Strength Bourbon and Scotch
I've noticed that cask strength whisky is getting sort of popular these days. I can't say that I love either of them although I'm a huge fan of both products in their tamer forms. I really appreciate the pungent flavor up front of a cask strength although I find the finish, due to the heat, border-line painful. Moreover, I've been told that adding water to cask strength is to essentially defeat the purpose. So I'm looking for opinions.
To me the main attraction of cask strength is the lack of chill filtration. It definitely affects the flavor and mouthfeel, in my opinion. And the thing that goes hand-in-hand is that cask strength scotch offerings include the independent bottlers. Some of the Cadenhead whiskies I've had were stunning. And Booker's is one of my favorite bourbons.
As for diluting, I think the idea is to nose and taste a little neat at first, then dilute. You'd pretty much burn out your palate rapidly otherwise.
On the contrary, I don't think the purpose of cask strength is to taste the highest possible alcohol content...if that were the case you could just drink grain alcohol. The purpose, rather, is to taste some of the raw material that the distiller has and then play the role of the distillary master yourself, adding the amount of water you think necessary to create the best drinking dram.
There are some cask strenth whiskies, George T. Stagg bourbon for instance, that I wouldn't add anything too. There are others, such as Laphroig 10 yr c/s, which really open up with a few drops of water (I wouldn't add more than a half teaspoon per shot, but different people have different tastes).
Another option, if the finish is your main concern, is a water chaser.
Remember also that most cask strengths are 10 to 15% more alcohol than regular bottlings, so the addition of a few drops of water will still leave you with a powerful drink.
I love the cask/barrel strength liquors for a variety of reasons which sku and ted already said. I also feel the key to any good spirit is adding just the right amount of water for it to open up and release the full flavors. For each spirit and individual the amount is different, but adding some water is necessary to enjoy the full taste. When the spirit is over around apx. 70 proof the high alcohol numbs your taste and smell so that you can't enjoy the full flavors and especially the nuances, these become available as you slightly water down the spirit.
Some cask strengths almost require a little water. Scott's Selection has (or had) a Glenlivet that is bottled at about 168 proof, or at least close to 160. Drinking ti without diluting it or chasing it with water is inviting trouble. While drinking the same brand's Linlithgow neat is manageable, as it is about 120 proof.
Cask strength's are rawer, simpler, as they come from the barrel. If you dilute it, it is you deciding how much to dilute it, not being handed something and having to accept it as someone else thinks it should be.
Cask strength whiskies are the new marketing fad (succeeding 'finishes'). Cask strength whiskies are made to have water added. The idea being that the distiller adds water to lower the ABV to 40-43%, why not allow the consumer to add what he thinks is the appropriate amount of water. The alcohol content is so high that if you don't add water, you taste booze and not the whisky.
The biggest advantage to bottling at cask strength, or barrel proof, is that chill-filtering is rendered unnecessary. As noted above, non-chill-filtered whiskey has an oilier mouthfeel and more flavor, because it is congeners and esters -- flavor elements -- that get filtered out in chill-filtering. Filtering became popular in order to allow low-proof bottlings (under 100 proof) to be chilled without developing an off-putting haze. Although the haze is nothing but the aforesaid congeners and esters, they are unsightly, and many folks don't like it. Thus, virtually everything today under 100 proof is chill-filtered.
By all means, add some water -- which also serves to stretch your bottle and make it last longer.