From the ability to remove the lid from a tight jar, to delivering a firm handshake after a business meeting, having a strong grip can be very helpful in a person's everyday life.
If you are interested in developing your grip strength, I highly recommend that you consider the "Captains of Crush" series of hand grippers from Iron Mind. Their all-metal construction feels very solid in your hand, and with ten different strength levels ranging from 60 pounds all the way up to 365 pounds, everyone is sure to find a hand grip to challenge and develop their current hand strength.
Each hand grip is labeled on the bottom of its knurled handles to indicate the strength level. When you first begin to use these, you may find that the knurling on the handles may seem slightly harsh and uncomfortable, however with continued use, your hands will get used to the feeling.
I've personally been working with various strengths of these grips for the past year, and in that time my grip strength has increased considerably. I'm currently working with the level #2 grip (195 lbs.) with a long-term goal of reaching level #3 (280 lbs.).
For anyone that is interested in strengthening their hands, these are highly recommended.