First, you will increase your calculation ability and avoid missing “long moves” such as Qg1-a1-a8 in variations, very often a mistake of many chess players. In addition you will “feel” the geometry of the chess board much better (lines, diagonals etc.) It becomes natural.

At the high level, blind training can help to keep deep concentration for a long time. An absolutely necessary quality of Masters or Grandmasters. For example: before my biggest success in the Cup of Russia (Tomsk, 1998), where I shared 3rd place in company of 6 GMs, I gave a few blind simuls, each with 3-5 opponents. As a fact: for many strong players it is practically not important how they play chess – with looking at the chessboard or without calculating the moves in their minds. The probably most famous example is – GM Vassily Ivanchuk, who only takes a look at the board when pieces are moved.

The Chess Eye is unique and contains several kinds of exercises where any player can find a good one for his level. Your rating will
improve if you keep on exercising, make your way from #1 to the end."

IM Denis Salinnikov