Saving seed from hybrid vegetables in the garden, will produce seeds which will grow into plants which may be quite different from their parents. It is a lottery, and always surprising to see what the combination turns out to be. They may have great hybrid vigour, growing strongly and healthily. Some hybrid plants have unusual, but useful, disease resistance. Other hybrids can yield heavily, or not at all!
Plant breeders spend years producing hybrids and looking for beneficial features. This is why hybrid seeds are so expensive. But the plants grown from the hybrid seeds will not produce seeds which are true to type. The seeds borne by hybrid plants will very rarely produce plants similar to the parents.
It is, therefore, not advisable to keep seeds produced from hybrid vegetable plants in the garden, because of the uncertain outcome. It is fine to keep seeds from Heirloom vegetables & other open pollinated varieties.
When saving vegetable seeds from the garden, follow the correct procedures for saving vegetable seeds.