The restaurant and Instagram
There are small mom and pop hole in the wall eateries that have some devoted followers. They can use Instagram better then many chain restaurants. They probably cannot make changes to their menu often for the cost. But they can use Instagram to remind people of specials and hours of operation that they have. They can show a picture of a stake or vegetarian kabob. They can show different ways that guest want on their meal.
There are special events that might be happening and the restaurant wants to promote there up coming event with an invitation. There are games or TV shows that they invite people to come out and watch as they are enjoying some drinks and food. They can get specials and happy hour deals out their for different people.