Whether you have raised beds or not, the key is to add organic matter to your soil so water and nutrients don't go straight out the bottom. The sandier the soil, the faster water will respond to gravity. This is true in a raised bed or in a bigger area of topsoil. What you don't want is soil with a clay subsoil that won't allow water to drain. Plants that will do well in soil that has little or no drainage are the same plants that do well in a swamp. The ideal soil has its own nutrients, holds water well, and also drains well. Materials that are all organic matter or all sand don't work well as soil unless there are amendments: peat moss, wood chips, and sawdust come to mind. It's why soil that has been continuously cropped with corn is a disaster: the organic matter is reduced so much that the slightest rain brings erosion. No-till came along to help with the erosion, but it doesn't solve the real problem of soil depletion.