What does it mean when there are two addresses listed in the data sheet for a particular register?
One (the lower number) is the IO port address which is used when using the IN or OUT op-code. The other (higher number) is the memory mapped address.

Different methods of access are more programatically efficient depending on how you are manipulating the values. For instance IN and OUT are more efficient at setting or reading the entire register value, but SBI and CBI on the memory mapped address are more efficient when manipulating individual bits.