Smart meters allow data collection in half hourly (HH) periods (the standard measurement period in the energy retail industry). A HH report will take the format below, but on a daily basis.
Period: Energy (kWh)
1 (00.00-00.30) 1
2 (00.30-01.00) 1
3 (01.00-01.30) 2
Repeat measurement for 48 periods during a day.
This allows your energy supplier to know exactly when you are using energy, and how much.
This is useful for them in two ways..
Firstly they have more data to allow them to trend and forecast energy consumption more accurately over time. This give the grid more stability as National Grid will be able to dispatch additional energy onto the grid when required more accurately, saving costs as they won't have to overestimate demand by so much, which means they won't have to overpay for energy they won't need.
Second, in the coming years, due to the increased penetration of renewables into the UKs energy mix, there is likely to be a surplus of energy during the day (most are in work/out of their homes, solar generation will peak during mid day), and a deficit during the evenings when the sun has gone down, possibly further exacerbated by low winds that day, people will also be home from work having showers, cooking food, watching Corrie, so energy demand will peak. Smart meters will allow energy supplier to charge us consumers different tariffs at different time of the day, as they will know how much and when we used it. High generation, low demand during the day...cheaper energy. High demand and low generation during the evenings...expensive energy.
In short, having a smart meter now isn't really an issue as you will get a fancy little display in your house so you know how much energy you're using an how much money you've spent on it today/this week/this month.
Having a smart meter in future will open you up to the variable tariffs, which will be inevitable in a few years. I'm not sure if this is a bad thing. With a smart meter you will either pay for exactly what you have used, when you have used it. Without a smart meter, will they have to assume an average pence per kWh, and charge you that on all energy consumed? This cost may work out to be higher, than paying for exactly what you've used.