One of the especially intricate and complex areas of Halacha is that of "Shinui Makom" – changing one’s location in the middle of a meal – which the Shulhan Aruch discusses in Orah Haim 178. Many different variables will determine when it is permissible to leave one’s place before reciting a Beracha Aharona or Birkat Ha’mazon, and whether one must recite a new Beracha when he resumes eating in his new location, or when he returns to his original location.
Here, we present one very straightforward Halacha which is agreed upon by all Halachic authorities, namely, one may change places within the same room in the middle of a meal. As long as one does not leave the room, he may change locations and then resume eating in his new location without reciting a new Beracha. For example, if in a synagogue or study hall there is a coffee machine in the back of the room, one may make his coffee, recite the Beracha and begin drinking in the back of the room, and then bring it to the front of the room and continue drinking there without reciting a new Beracha. This applies even if one changes locations within a very large room, like a banquet hall, and cannot see his original location because it is obstructed by furniture, a pillar, a vase, or some other object. At weddings, for example, if often happens that a person begins eating in one location, and then sees a friend at a different table and moves next to him. This is entirely permissible, and he does not have to recite a new Beracha when he resumes eating at his new location, since he moved within the same room. This is permissible even if one had no intention when he began eating that he would later change locations.
This Halacha is discussed by Hacham David Yosef, in Halacha Berura (vol. 9, p. 203; listen to audio recording for precise citation).
Summary: One may change locations within the same room during a meal, even if he cannot see his original seat in his new location, and even if he did not intend to move when he began eating, and he does not need to recite a new Beracha when he resumes eating at his new location.
