I use them all the time. The info I've read is that the body's making of enzymes drops after the age of 27, which the early enzymologists equated as the number which old age begins, exactly because of this. This drop continues until 35, then the body makes them in appreciable amounts only when eating. So I use them liberally when eating to minimize the burden on the body and maybe slow down the aging process, and I also think this is a good idea anyway with all the processed ingredients found in many foods today.
You may not know how much a role enzymes play in keeping you healthy, so I recommend the book "Enzymes: The Fountain of Life" by doctors Lopez, Williams and Miehlke for more info. Also, pay attention to how many times the word enzyme appears in any nutrition or supplement article here on T-Nation and you begin to understand their importance.