It's very easy to put a sinister spin on this...
But think about it for a moment. In normal operation, demand management works by reducing demand within certain parameters defined by the houselder or the device - they're not going to shut down your fridge completely but they may defer its cycle kicking in for 5 or 10 minutes to smooth the load.
In the extreme case of a catastrophic supply failure such as a black out, if end users can be shut down remotely and then progressively brought back online, you can restore power much more quickly.
What's the benefit of demand management to you the householder? By smoothing out demand, less plant is required to generate our electricity at peak times (very inefficient, very expensive). It also enables a much higher penetration of renewables on the grid (something Lewis is very scared of). This will keep costs down and allow for a much more flexible, diverse electricity supply.