Of course most addresses don't have any coins in them anymore.
An address that has not had coins spent from it is more secure than one which has. Therefore, the most prudent thing to do when spending a partial balance is to send the rest to a new address that you also have the key for.
Sample size of one, most of the addresses I've used now have a zero balance. But I know this is common practice for many people and businesses as well. Not to mention mixers and other cases where coins rapidly change hands.