The chairs in your restaurant can make as much of a difference as the food you serve to those sitting there.
McDonalds has been proven to make their furniture as uncomfortable as possible for the customer, without actually making them feel put out. The under-sized, uncomfortable chairs are designed to get the people out as quickly as possible to free up the table for the next family to squeeze themselves onto.
Ikea's floor plans are designed to confuse you, so that you get lost and end up spotting things you never knew you'd wanted. Likewise with escalators between floors that you have to navigate a small marathon to get between.
All this is done completely separately and with little to do with what the company actually sells or offers. Therefore, with your restaurant, you need to look at the target demographic, what you wish to give them and kit out the venue accordingly.
For a high-end restaurant aimed at class and style, restaurant chairs that look modern yet feel comfortable are the way to winning over your customers and furthering your business, making those in the seats want to stay put and order another of those champagne bottles.
A buffet restaurant, however, would do better with slightly less comfortable, smaller chairs. In line with the McDonalds ethic, the chairs will encourage people to not stay for more food, the small chair making them feel maybe more full than they are. Twinned with smaller plates to give the impression of having eaten more will nudge the customer in the right direction, often without them even realising.
There are, of course, many different circumstances, all requiring a slightly altered outcome, but knowing what to offer the customer in all aspect, not just the products you offer, can have a huge result on how your business operates.