The home theater system saves you time and energy. There's no figuring out what goes where and how with what wires. With a "theater in a box" you know the speakers are going to match for sound and the wires will all be accounted for with instructions and color coding to tell you how to hook it up. All that remains for you to have is a TV with audio outputs and AV inputs.
The name "theater in a box" also indicates another perk...its size. The system is designed to be small and relatively discreet. The DVD and receiver unit often come in the same unit and can be the same size as a DVD player alone. The speakers can be quite small and mounted unobtrusively around your room.
Price is another added attraction. With a home theater system you get everything at a reasonable price at your local electronics outlet. Systems start at $200 and can go up to $2000, depending on the size of your room and level of AV sophistication.