Yes it is a good practise to close and destroy the record set.
A couple of reasons that we close and destroy the record set are:
1. To reclaim memory on the client machine. When we keep the record set in memory for no reason we are wasting the memory which can be used for other things.
2. To close the connection to the database. When we are using a RDBMS such as Oracle or SQL Server each connection to the database takes memory on the database server. By keeping the connections open we are holding memory in use for no reason which could be reused for another connection or process.