I know currently when you check the "Do not send multiple emails to the same email address" checkbox you can send one email to multiple people by using the "Primary and spouse" field.
The difficulty is that for some people the spouse may be in that particular mail out and for some they may not.
What I would find helpful is a field that automatically combines all names in the mailing list that share an email address.
If Joe and Joanna share an email address and are both in the email list the field says "To Joe and Joanna"
If however Sam is in the mailing list but his wife Samantha isn't, the field simply says "To Sam"
Thanks for the email.
I've submitted a feature request for a %recipients_full_name% placeholder for this.
Hope this helps,
+1 for me as well