SparklyKid. It's quite straightforward to me. Some examples off the top of my head:
1) If I know the cost of using the tumble dryer on Economy 7 I can decide whether to shove the laundry in before work and get it out of the way or whether to risk/go to the trouble of putting it on the washing line.
2) If the kids had left their TVs/computers/lights/fans on I could point out the costs to them. Maybe I could even see the info via my phone from work.
3) If I know the cost of leaving on an outside light over night I could decide whether the pleasure i get from seeing a lovely garden when i look out at night or deterring burglars is worthwhile.
4) if I know the relative cost of heating up my water by immersion meter on economy 7 or boosting it at day rates for a bath at night I can compare it with the cost of using the gas boiler.
Maybe I could think of better examples if you asked me again tomorrow, but there is no doubt that it's far better to know the costs and make informed decisions about turning things on or off than to get caught out by an unexpectedly large and possibly unaffordable bill.
I realise some don't worry about their bills (and actually i could afford my bills if they trebled but I'd rather use the money for something better) and some are so familiar with the power consumption of individual electrical items that they can do all the necessary calculations in their heads, but for others the info from a smart meter is invaluable or at least interesting.
There is no downside to a smart meter provided there is no charge and it doesn't force you to stay with the wrong supplier.
Of course there is a completely separate discussion that could be had about whether the overall costs of the roll out is justified by the benefits or whether it was wise to roll them out before the new generation meters are ready, but while they are being give free why ignore them if you want them. For those who don't want one or see the point that's fine, but it's wrong for them to assume people who benefit from them are foolish/mistaken.