Keeping the water flowing from the roof and gutter system is what the downspouts or leaders do as part of the gutter system. If they do not drain well you cn wind up with over flowing gutters from clogs at the top or too much flow at ground level not handled well. Drainage systems parts often are a second thought when the house is first built. Over time it becomes clear with observation if there are problems with down spout drainage. Solutions can be as simple as cleaning of the system at the top and all bends, or adding to the system.
Rainwater that drains onto soil near your home from the downspouts is generally not a problem if you have sandy or very well drained soil. Here splash blocks may be all that is needed. However, poorly drained soil, pavement and patio's that prevent good dispersal of rain water. With non porous serfaces or clay soils that don't drain that well basements and crawlspaces can become indoor swimming pools in periods of heavy rainfall or sustained wet spells.
Downspouts drain water to the area of the foundation and if there is no slope away from the foundation it can remain there and soak the soil along the foundation wall. With good sloping away from the downspouts the water will be harmless. Overtime many changes occur that change the slope such as setteling or landscaping that changes the slope resulting a storm or winter thaws bringing a wet basement. Older homes that have never had a problem all of a sudden are wet. I find this situation especially prevelant in older nieghbor hoods with relatively flat lots.
Drain tiles can stop soil erosion under downspouts. Many people do not realize just how much rain falls from the sky in a moderate rainfall. For sake of discussion, let's consider a normal ranch house that has an attached two car garage. If the structure measures 30 feet by 66 feet and has a 2 foot roof overhang, there is 2,380 square feet of roof ready and waiting to catch rain drops. A moderate 1 inch rainfall will generate 1,483 gallons of water on this roof. This water will hit your splash blocks and enter the soil about 30 inches away from your foundation. If your region receives 40 inches of rainfall a year, you will inject about 59,320 gallons of water into your wife's gardens. That might be a little overkill, don't you think? If your foundation is currently leak proof, your sump probably accepts a good portion of this water. If the sump pump discharge pipe merely dumps the water along side your house, you end up recirculating this same water time and time again. This wastes electricity and leads to premature pump failure. I feel that your storm water and sump water should be piped away from your house. Some urban areas allow this water to be connected to public storm sewers and water retention basins. If this is not available, pipe the water to the lowest portion of your lot where it would have drained naturally before your house was built.