it puts pressure on your opponent, and its a psychological thing that makes you look much better prepared
Playing Fast-is it Strategy?

it puts pressure on your opponent, and its a psychological thing that makes you look much better prepared

Shatters opponents concentration just like glass, Although it doesn't work on everybody.

it might be intimidating,but it creates mental time pressure on you,also making your moves much less calculated.take all the time you need to find a good move.

The clock is an important and oft-neglected part of the chess puzzle. We know that exchanges benefit someone with less space, so we should avoid that if we have the space advantage. Similarly, if a person has very little time, we should likely keep the position complicated, because a position with obvious moves is easier to play in time trouble. That said, there are times where exchanging pieces even with a space advantage is simply winning, and there are times when simple positions in time trouble are also winning. Don’t let time, space or any other consideration stop you from playing good moves.
I use to dismiss the clock element of chess, but my eyes were opened when someone said the following. When you look at many Super GM games, you often reach a point around move 30 where the annotator will say, “Black was under pressure and in time trouble, and so he committed the following blunder.” An incredible number of games follow this pattern, to the point Super GMs lose to i) opening novelties, ii) time trouble and that’s it.

Why?
My guess is that some think its a mental advantage. I dont understand it, but some do use it. For me...If you want to blast out a bunch of moves quickly, go for it. Its still a game of chess.

playing fast in the opening is only good ,if you really know the opening
Or you can think on your opponents time or play natural developing moves
Beware of natural developing moves.
1. e4 c5 2. Nf3 d6 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 g6 6. f4 consider Black's reply 6. ... Bg7. It's the most natural developing move on the board. Is it a GOOD move?

There's nothing wrong with Bg7. If you think e5 wins the knight, it doesn't.
I would have played 8. Bb5+ and 9. e6.

There are two strategic reasons to play fast:
1. Psychological - as has been previously mentioned here.
2. When your opponent is short of time and you don't want him thinking on your time, for example when he's winning and you have a plan you hope he doesn't see-though so you don't want him to be able to think on your time.
Why?