Another problem that occurs when spacing is to close together is there is no space for water, snow, dirt, twigs and leaves to fall through. Cleanliness now becomes a problem because falling precipitation coming off trees and leaves will deposit sap and dirt. With no place for run off your deck will be covered in dirt and sap creating big clean up jobs every time it rains. Standing water will also lead to excessive mold growth.
Any place that sells decking should always provide spacers with the materials. Every product is different and expansion and contraction will be different with every product. This is why the spacers should be from the name brand decking company you bought your materials from. When in doubt you should always call the manufacturer to ensure you are using the correct spacer especiall when you are decking in Suffolk County NY.