Variable billing can save you a lot of money, especially if you have your own generation capacity - PV panels, wind/water turbine etc - by making it possible to schedule maximum use during low-price (usually during the night, sometimes in the middle of the day) while minimising use during the morning and afternoon peaks. Play this right and you'll end up with negative electricity bills (in regions where small-scale producers can sell to the market, Sweden being an example of such). Contracts often stipulate that small-scale producers can not produce more kWh than they consume. By scheduling consumption so that it either falls during times of excess own production - which makes it possible to avoid paying energy taxes and transport charges or when the market rates are the lowest you end up with as low a bill as possible. At the same time you can decide to export power to the network when you happen to have excess capacity at high-price moments thereby maximising income from electricity sales. Play this right and you'll end up with net-negative electricity bills even while producing no more kWh than you consume.

I'd look more into it - Octopus Agile can save you a heap of money, doubly so if you have Solar + Battery so can more effectively load balance.

And Intelligent Octopus Go is a variable rate - 7p 23:30-05:30 (and any time during the day your EV is plugged in and there's a glut of green cheap energy on the grid).