One or two weeks ago, seating plan to me is absolutely necessary, no question, no discussion. Everyone should be assigned a seat, less chaotic, more efficiency everyone is happy. Now I'm thinking a bit more and want more critical arguments.
Question 1. Why do need to do this?
The venue is a restaurant. When the weather is good, we will have the dinner outside. When the weather predication says otherwise, we will have to sit inside, which is not very ideal. the floor plan looks like this.

There are four different rooms (connected though). No matter how we assign the seats, someone will be forced to be assigned in some other room that cannot see the main table. This sounds very bad. I really had no solution to this problem until now. Here is the solution. why don't I just throw away all seating charts and therefore nobody will be assigned to another room. I will also get rid of the main table. On every table, I can reserve two seats for bride and groom. That means we walk around during the dinner from table to table.
Question 2: Are there more seats than total number of guests
Yes, there can be 150 seats if all the rooms are in full use. we will have probably 100 people, at most 120 people attending.
Question 3: How is catering done?
Actually it's the restaurant that recommends me not having a seating plan (and it's super hard for me to accept and to imagine how this can work) so they really have no problem with it. The serving from the restaurant is something they called "flying dinner". It's not a buffet style. It's also not plated. For every course, waiters will walk around with small plates along with the forks. (They make sure no knife is needed). For example, there can be three different varieties in the first course and everyone can freely choose what they want (even multiple times). The main course probably have one variety but people can also choose to have it multiple times. Guests will be encouraged to mingle and move around during the entire dinner. Wherever they are, they can be served with food and fork. We also don't need to consider vegan vegetarian or other food allergy. This is because people can just choose. Basically, waiters can walk around with glasses of wine in the cocktail time, they also walk around with food plates in the dinner time. Here are some photos to give you an idea what does "small plates" mean.
fish (main course small portion)
soup and tartar
dessert
Question 4: How about toasts, wedding videos, cutting cake, first dance if guests do not sit in one room?
I am thinking about having all these in the Festsaal, the largest room in the floor plan. There are enough place for people to stand (only stand, no place to seat 100 people) and there are projectors. The dance party can also be there. So now I imagine in between every course (before the first, before the second, before the third, before the dessert, after the dessert), people are informed that the toasts will happen in the Festsaal and they can move there and listen to the toast while standing. Then they move to a new seat. (or probably just move back to where they were).
The first dance and dance party will also happen in in Festsaal.
Question 5: How about parents and grandparents?
We will probably have a specific family table. Other than that, no charts.
Question 6: Do I have more concerns?
I guess no seating charts are very unusual and they probably always(?) happen in very small receptions where everyone knows everyone. This is not our case. We are expecting 80 ~ 100 guests from all round the world. They don't even speak the same language. I am still quite concerned with the possible chaos.
Forcing people to stand and watch the toasts, watch the first dance is probably also wired.
And how about guests with kids? They probably cannot move too frequently?
All in all
I was super concerned about having guests in different rooms and I had no solution before. Now I think I came up with a good solution and this can work out. Moreover, all such plan is just for bad weather. In good weather we will have enough place to seat everyone in one area. Of course we need to move guests inside to the dance floor and there we still want guests to move around and mingle during the entire dinner. I write this entire post to make myself more clear and also hope to get VERY CRITICAL comments.
-- Something I haven't think of?
-- Have you had similar experience?
-- Any better suggestions?
We are still in the phase of choosing venues so we can still choose other places. This venue is great (date, flexibility, price, outdoor dining option etc) but this issue, having to seat guests in different rooms, is the major downside, which almost kills the venue. We also have other options with other advantages and disadvantages. So what do you think? Thank you so much for reading this long and looking forward to your reply!