A subsoiler is a tillage tool which improves the growth of all crops where soil compaction is a problem and makes the soil more productive by breaking up the hard pan that forms from rain, long term non-tillage or heavy compaction from extended use. It gives moisture a chance to penetrate deep below the top soil to be held in reserve for the dry spell ahead.
In addition a Subsoiler can provide a drainage path for low spots so the water can seep to a different location. For example you have an area that the water always collects in and you use the subsoiler to rip a path to a drainage area. This will allow the water to seep in that direction with minimal disturbance to the top layer of ground.