This question has come up before but probably got lost in the many posts on these forums. Squash, zuchinni, cucumbers, okra, egg plant, and many other fruits are always picked before they are ripe. Ripe means the seeds got ripe, and that means the fruit is virtually inedible. So for these three crops, pick as soon as the fruit is large enough to suit your fancy, and the earlier the better. The closer these fruit get to ripening, the more energy it takes from the plant, them plant slows down production, becomes spent, and dies. So just like dead heading flowers, if you want lots of squash and cucumbers, keep the vines picked, and keep them picked when the fruit is still small. In the early rapid growth phase of these plants, the fruit can get pretty large and still not get overly seedy, so eat those fruit, but intentionally letting them get large, IMO, is not a good strategy. Later in the season, even a modestly sized fruit will begin to get woody, tough seeds. Pick often, pick small, and be rewarded with a long lived plant that gives an abundance of fruit.
Eclectic gardening style, drawing from 45 years of interest and experience. Mostly plant in raised beds and containers primarily using intensive gardening techniques.