Are you talking about the Airport Standby List? It really only helps right before the flight. As the flight begins boarding, you’ll see how many passengers are on the standby list and how many seats are available. As the gate agents assign seats to the standby passengers, you’ll see the numbers changing — the number on the standby list will decrease while the number cleared increases.
Days ahead of the flight, you won’t really be able to know from this list if you’d get on, but it gives you some idea of how many seats are available.
A good use of this list is also looking at it after the flight departs. You can see if there were uncleared passengers, or if everyone on the standby list made it on the plane.