The central benefit to finding and buying a HTIAB is the simplicity and cost-effectiveness of staying with a single manufacturer brand and overall ease of setup. A separate receiver, speakers, DVD or Blu-ray player can add up to a fairly expensive shopping list, and putting all those things together can be a hassle when it's time to figure out which inputs and switches connect to which functions. By limiting the number of combinations, an all-in-one makes finding the correct signal easy -- and by limiting the amount of hardware involved, it can take the pressure off your wallet, too.
On the other hand, you may find yourself yearning for a greater, more complete sound than the HTIAB offers. Every living room is different -- and when you upgrade to a larger TV or Blu-ray player down the road, you may find that your old HTIAB system is lacking in sheer power. A sound bar system is a great, cost-effective alternative to more complex systems, but moving that home theater into a new home or larger area in your house could turn that benefit into a drawback.
And then, too, there's the risk of wear to any lower-priced technology, which, when combined with the centralized nature of your system, means that you could be throwing the whole thing out later. A damaged onboard DVD can easily be replaced with a separate player, for example, but a damaged receiver -- or even one of the speakers -- can invalidate the entire system.
The risk isn't so much that the technology will become obsolete -- speakers don't work that much differently now than they did 100 years ago -- but that the system will keel over of its own accord. Buying replacement speakers or individual components is sometimes possible, but at some point, the cost of replacements may invalidate your entire reasoning for getting the system in the first place.
Remember: The industry thrives on your purchases and your purchases alone, which means that it's in their best interest to keep you buying upgrades. Just because you're satisfied with the quality of what you bought doesn't mean it won't break somewhere down the line. Take these future possibilities, and your current needs, into consideration -- as when making any entertainment purchase -- and you won't be disappointed later.