In general, barbecue is cooking using wood on an unheated flame in order to raise the temperature of the meat that is being cooked to an acceptable temperature gradually in order to ensure that there is no loss of moisture (i.e. the tenderness) from large pieces of meat.
Most barbecue cooks make use of indirect heating (i.e. the fire source is located off the cooker's chamber) instead of direct heating (i.e. the source of heat is located directly in the proximity of the cooker) to combat this problem. Many kinds of BBQ smokers are there in the market and offset smokers are the most popular kind that people prefer to buy.
There are many examples of indirect barbecue smokers as opposed to direct-style barbecue smokers. There are many different variations and alternatives for smokers.
The choice of smoker depends on a variety of factors such as the availability of wood as well as the price of purchasing charcoal versus the availability of wood, space to store the cooker when it is not being used, etc.
If you live in an apartment, you could find it difficult to justify purchasing an enormous offset cooker not just because of an absence of wood but an absence of internal storage space for the cooker when it is not in use.