I would say that if the result of the tasting is to produce some sort of independent score, then they must be blind - the only way to really concentrate on taste and smell is to go blind, otherwise you can never account for the 'emotional' side kicking in and effecting your judgement.
One man's creamy Macallen is another's oily spirt, one man's bop between the eyes is another's Laphroig cask strength!
If the tasting is for fun or to introduce new whiskies to friends, then you don't need to go blind. The story behind the whiskies always warms the taste buds.
I read somewhere that blenders have the blandest offices going, all white walls and no windows so that, if the sun is out and a good looking blond walks by putting them in a happy mood, they don't turn to taste an ordinary whisky and say 'life is great - that's a great whisky'!!!