I think that is a very good idea. Keep as much of the rainwater on your property as possible. Soil, mulch, swales and hugelkultur mounds, are among the best places to "store" rainwater...
I know the answer is "it depends," but for how long can the soil retain water? This is my garden area (actually a paddock, but I have no horses):
The trail to the right has a lot of runoff during our brief winter rainy season, when I don't have anything growing in the garden anyway. If I could divert the rain into the paddock and flood it, could that water be available to my plants later? Like in the summer? Or would it just drain away below ground?