Pore space in soil is the volume of space that can be filled with water or air. A large pore space is normally filled with air while smaller pore spaces are primarily filled with water.
There are different trade offs depending on the pore spaces. Soil with larger pore spaces has access to lots of air but is not able to hold much water. As such, it needs more access to water at greater frequencies.
In the same way, highly compacted soil or that with smaller granules of soil can hold more water, but need frequent aeration in order to maintain a healthy balance that is beneficial to growth.