I'm not sure if this is true of every vehicle with multiple sets of doors, or if this is a feature of certain vehicles. That said, some vehicles let you unlock the front and back doors, and lock them, from inside. Great.
At least some of these vehicles, however, can't unlock or lock the back doors from the outside. This may be an intended feature, albeit a very annoying one. There have been many times I wish I could unlock the back doors of my vehicle from the outside without messing with the front doors, and I'd love if the ability to open the back, alone, from the outside could be added in.
Similarly, adding in the ability to look in the back seating area from the front in all vehicles, and the backseat to the front in most, would be really helpful.
Reasons why not may include:
It forces you to unlock and keep the front unlocked, allowing chances for people to steal your vehicle, or at least look like a jackass when they're caught trying to start it.
Not all vehicles have outside locks on the back.
Reasons to include:
Some vehicles are far too annoying to check the back seats for whatever reason you need to.