"The pro that I can see is that you will have a better idea of how much each electricity appliance costs so you may adjust accordingly if you think that eg the tumble drier could be switched on less to save money."
The big disadvantage I see is that many people confuse energy with power. What you pay for is energy, which is power multiplied by time.
They all too readily latch onto the high power devices like kettles or hairdryers and assume that must be where the money is going even though they are only used for a few minutes at a time. In reality, the big guzzlers are the appliances with much a much lower power consumption that are on for hours on end. The fridge and freezer are usually among the biggest consumers in most households, unless you're heating by electricity.
A good example of the problem is those who festoon their kitchens with halogen lamps and then wonder why they bill has gone through the roof. They might only be 50W each, but multiply that by the number of lights, and then by the hours they're left on for.....
You will often see it recommended that you switch off all but one appliance in order to use a meter to measure its power consumption. The pitfall with that is with any appliance that has a thermostat, such as fridges, cookers, heaters etc. you will only get an accurate answer if you're either careful to measure over one cycle of the thermostat, or else average over a period much longer than a single cycle.
All in all I think that smart meters are an expensive gimmick that are likely to mislead those who don't know what they're doing. Nobody has studied what the long term benefit will be, long after the novelty of playing with a fancy meter has worn off.
