Led by an expert, they let you know a little about the wine before you taste it. Great for newbies to the world of wine.
For the higher level wine professionals, you know nothing about the wine you're tasting. The taster (a higher level sommelier) can determine the age, origin, grapes and quality of the wine.
The same wines made by the same vineyards produced by the same winemakers but vary in vintage (the year the grapes were grown). An ideal way to show how wines age and one of the most interesting tastings.
Several wines from the same region and the same vintage (year the grapes were grown). Say five 2001 Cabernet Sauvignons or four Burgandies from 1999. Helps you better understand the concept of "terroir".