As mentioned, rectangular tables present a certain advantage in terms of capacity that round- and square ones do not. Imagine having to place all the diners to be seated at this elongated table at a round one – you’d have to have a pretty big round table!. For big dinner parties, it’s best to opt for an elongated/rectangular table, as you get more space for chairs and guests.
The style of table you have selected will directly impact on which chairs will work. For example, you'll often find that circular tables can accommodate far wider seats and even high backs will work well, wheres more angular designs often require compact chairs, as they'll have legs to contend with.