Although some scientists classify as many as 20 senses, when childhood educators talk about "developing the senses," we typically mean developing the five standard senses: sight, hearing, touch, smell and taste. In addition to honing these senses, educators care about sensory integration, which is the ability to take in, sort out, process and make use of information gathered from the world around us via the senses.
Why does it matter?
The better kids are able to tune and integrate their senses, the more they can learn. First, if their senses are sharper, the information kids can gather should be of greater quantity and quality, making their understanding of the world more sophisticated. Further, until the lower levels of the brain can efficiently and accurately sort out information gathered through the senses, the higher levels cannot begin to develop thinking and organization skills kids need to succeed. Senses also have a powerful connection to memory. Children (and adults) often retain new learning when the senses are an active part of the learning.
So, if kids have more sensory experiences, they will learn more, retain better and be better able to think at a higher level. Makes the days they get all wet and dirty in the sandbox seem better, doesn't it?