In physics, units matter (just ask the Mars Climate Crasher Orbiter). They put a context on the number. That isn’t always enough, because you don’t know if the number is big or small unless you compare it to a familiar quantity, which is why it’s a good exercise to be Putting a number in its context

[I]s the failure rate exceptional? A figure means nothing if it has no context: 600 pregnancies sounds like a big number, but there is no way to know what it means unless we know how many women had Implanon, and for how long.