Switch stacking might just reference a series of switches "stacked" within a cabinet interconnected either in a star or daisy-chain using their normal edge ports. Or, it might refer to special vendor architecture for interconnections of switches beyond using their ordinary ports.

Assuming you're asking about special vendor architecture switch stacks, Massimiliano's link provides the details for Cisco's StackWise and StackWise+. In brief, the major purpose of some special vendor specific switch stacks is to allow multiple physical devices to function much like one physical device. Other technology might allow multiple physical devices to be managed as one logical device (e.g. Cisco clustering).

Having multiple switches function as one has implications for things such as STP topology and router topology (if L3 switches).

Depending on the architecture, other features might also be provided by a switch stack. For instance, StackWise (if both rings connected) allow loss of one memeber of the stack without breaking the stack. Other stack architecture might not support this. (I don't recall whether Cisco's earlier GigaStack did.)

Physically, a stack might provide higher bandwidth between stack units than could be acheived using their oridinary ports. This too is a feature of StackWise.

In summary, for the purpose of switch stacking, you'll first need to determine what type of switch stacking you're discussing, and if the vendor specific kind, look at the features provided for it by the vendor.