Good article by Chuck Cowdery in the current Malt Advocate on the nature of continuous distillation and its role specifically in the manufacture of bourbon. A representative of Vendome (the renowned still manufacturer in Louisville) is quoted that in the last 45 years, the amount of water in mashes has fallen by approximately half (from 44 gallons per bushel originally to mid-20's currently).
This is done to economise on energy costs (it costs less evidently to heat less water).
It seems a still can vaporise the thicker mashes just as well, or maybe the extra cost to do so efficiently is much less than to process a mash holding 44 gallons per bushel.
I find this interesting and I wonder if the taste of new spirit is different when made in the newer way.