There is a limit to how much solar power local grids can accept without grid upgrades. Solutions are being developed and implemented, but there will be constraints until then. Solar export limiting is a useful way to reduce the problem because it can allow many homes to export most of their surplus solar energy.
In the Ausnet area, for example, the inverter size that can be connected to their electricity grid is usually 10kW per phase, but export limited to 5kW per phase. So, if you have a system that uses a 5kW inverter, there will not be any need to export limit this system. If you have a system that requires a larger inverter such as an 8kW inverter the system would need to export limited to 5kW.
The house would still get the benefit of 8kW but only 5kW connected to the grid – see also smart meters