to prevent the possibility of any of its being saved for use,
This shows their determination continued even the next day. They wanted every bit of tea destroyed. They refused to let the British tax go into effect in any form. The detail reveals commitment and follow through in their protest and beliefs. This also shows how little the colonists thought of the Brits. by wanting ALL the tea destroyed, this shows that the Brits mean nothing to them, and they have no problem having nothing related to brits in their new country. They also do not want to be defined by anything that has to do with Britain.