The more leaves you keep, the more energy is available to produce large fruits. If the runners are getting too long, it's OK to remove some of them, but try to keep lots of leaves for the remaining fruits. In short, it's fine to remove some of the fruit, but try to keep plenty of leaves to capture the sunlight. If space is limited in your garden, try to select compact vegetable varieties or buy the vegetables at your local farmers market.
The amount of fruit you get is directly related to the amount of sunlight captured by the leaves. It's perfectly fine to remove some of the fruit to increase the size and quality of the remaining fruit. It's commonly known as "thinning."
