The tighter you hold the golf club, the less speed you create. The less swing speed you create, the less distance you hit the ball. The more you grip the club with your hands (small muscles/tendons), the less you swing with your body.
Think of your body as the big muscles (shoulders/arms).
If you want to hit the ball farther, would you use your big muscles or your small muscles? Your big muscles.
Golf is not a game of power, but a game that relies on rhythm, tempo, and timing.
To establish these traits, begin with your grip, and how tightly you hold the club. Your arms should "hang" freely from your shoulders and be relaxed.
Your left hand should grip the club with enough pressure with just enough hold so you don't let go of it (for right handed players). The accompanying hand should in turn be placed on the club gently.
A related factor to your grip and the pressure you apply is your posture. The grip and posture are extremely important because they enable our bodies to swing the club properly.
The way we approach the ball is often the beginning of the problem.
A great many people stand up to the ball first, then try to set their posture without realizing that they are not at the right distance from the ball. I see many people who look cramped over the ball or are reaching out too far for the ball. These positions do not allow the club to swing freely or comfortably.
The proper posture will allow the arms to hang freely from the body. From this position, the arms can move freely throughout the swing.
Think of relaxing the hold of the club with your hands, and by having the correct posture, swing with those big muscles, and you will not only hit it farther, but straighter too!