The Inner envelopes help eliminate the potential for any awkward questions regarding your guest list. Who gets the plus one, who is invited, are the children invited, etc.
The inner envelope would get more specific with:
David and Sarah
Grandma & Grandpa
Mama & Papaw
David and Sarah
William and Guest
Sarah
Inner and outer envelopes are the more traditional option. If your wedding is black tie, classic, or just all-around formal, you may want to stick with having both sets of envelopes to abide by wedding etiquette. Your invitation suite will be absolutely gorgeous to be sure, but do you know how impressive two sets of envelopes are? They help set the tone for your event.
