Question about reserving main dining room.

I’ve been on several cruises but have never reserved a dining time, because I like to leave my schedule open so I can to make last minute decisions to attend shows, etc. My experience with walk-in dining has not been great. Not super friendly and extremely slow. I’m considering reserving a regular time this time to try out what it’s like to have an assigned waiter . My question is : how big of a deal is it if you reserve a time but then sometimes just don’t show up?