The spades or banana plugs also serve to make a good contact, and allow easier disconnection and reconnection. By fastening (soldering, crimping) all strands into a connector, you ensure all of the cable is properly secured. Stray strands have been known to short on speaker and amp binding posts. This would not be good!

While they may not have an affect on the sound, they are a good idea for a solid electrical and mechanical connection.

Regards,

BBIBH