I know a lot of people have very strong opinions on this topic and I found this question posted at the Emily Post Institute website. Emily Post, and by extension, the Emily Post Institute has been a defining voice in etiquette.
So, it is nice to know, for those of us for whom space is limited for a head table and for whom a sweetheart table is not an option, that we are still well within the bounds of proper etiquette!
The following was taken from the Emily Post Institute website:
Good afternoon,
I am wondering what the current standard is for head tables at weddings. Is it appropriate to just include the bridal party, or should an invitation be extended to their spouses and dates? Thank you for your advice!
Response from Emily Post Institute: It would be best to seat couples together, but if space prohibits it, make sure the spouse or s.o. not at the head table is seated with someone interesting they will enjoy dining with. And, if at all possible, be sure they are invited to the rehearsal dinner, too.