To add, it is always a good idea to confirm whether or not to use a voucher with a soda or other non-alcoholic purchase as, although we usually get asked, the server may default to using it if not aware otherwise.
At D+ you will receive 5 vouchers per person, and they are combinable - you can use yours for your spouse, and visa versa, as the case may be. The vouchers are automatically renewed every 24 hours at 5:00 AM. Any remaining unused vouchers are forfeited as they do not carry over. If at the end of the night we have any left over we will go to any bar and get unopened canned or plastic bottled beverages (beer, Truly, soda, water) to take back to the stateroom for future use so as not to lose the vouches. The only venue in our experience they are not accepted is a the Bionic Bar.
Depending on ship and venue, reserved seating is available in the main theater, the ice rink, and the aqua theater, and has been for a number of years. In our most recent experience it was balcony back center in the main theater, front center ice in the ice rink, and back center in the aqua theater. If you wish to take advantage of it, I would suggest showing up about 20 minutes or so early as they open any remaining seats up to general seating about 10 minutes before the show.
Enjoy your returning D+ cruise!