A grid-tied system is a basic solar installation that uses a standard grid-tied inverter and does not have any battery storage. This is perfect for customers who are already on the grid and want to add solar to their house. These systems can qualify for municipal incentives which help to pay for the system.
One disadvantage of this type of system is that when the power goes out, so does your system. This is for safety reasons because linemen working on the power lines need to know there is no source feeding the grid. Grid-tied inverters have to automatically disconnect when they don't sense the grid. This means that you cannot provide power during an outage or an emergency and you can't store energy for later use. You also can't control when you use the power from your system, such as during peak demand time.
But if a customer has a basic grid-tied system, they are not out of luck if they want to add storage later. The solution is doing an AC-coupled system where the original grid tied inverter is coupled with a battery backup inverter. This is a great solution for customers who want to install solar now to take advantage of incentives, but aren't ready to invest in the batteries just yet.
A customer can benefit from metering because when the solar is producing more than they are using, they can send power back to the grid. But in times when the loads are higher than what the solar is producing they can buy power from the utility. The customer is not reliant on the solar to power all of his or her load. The main take away is that when the grid goes down, the solar is down as well and there's no battery back-up in the system.