This article courtesy of Ohio State University Extension Services.
More information at www.bygl.osu.edu.

It is a good idea to harvest veggies as soon as they are ripe. Ripe veggies can "sap" a lot of nutrients from the plants for fruit growth and seed production. If left unharvested, the vegetable plants will slow down future fruit production, thus yield will decrease drastically. Timely harvest is not just good for the gardener, it is also good for plants. Gardeners will be rewarded with more fresh veggies. Don't wait until cucumbers or zucchini get too big! Keep on harvesting. This is also a good time to share the bountiful harvest with others. Donate excess vegetables to a local food pantry. Everyone wins in the end!