The inputs and outputs of the grid need to be balanced. A large proportion of the UK's grid inputs come from renewables - wind and solar - that can't easily be controlled. That's leading to increased supply volatility and so increased price volatility, which in extremis results in (previously unheard-of) negative prices.
Consumers aren't looking at prices in real time, but industrial users are. Let's say that you run a large cold storage facility. You need to maintain temperatures within a safe range, but that gives you some responsiveness to real-time prices - you could push towards the low end of that range when prices are low, or drift up to the high end of that range when prices are high. In effect, you're using the temperature of your warehouse as an energy storage system. The same would apply to many industrial processes that involve heating, cooling or pressurised fluid.
As we transition towards 100% sustainable energy, we hope to exploit much more of these non-obvious sources of energy storage through dynamic pricing and smart appliances. If you charge your electric car overnight, you don't actually care when it draws energy from the grid as long as your battery is full in the morning. A smart charger could wait until prices are low in the dead of night, or even feed back some energy to the grid during the early evening. You probably won't notice if your air conditioner or your heating drifts beyond the set temperature by half a degree, but the grid most certainly will notice millions of smart thermostats that can reduce grid demand during brief peaks.