Why is the reactivity series of metals important?

The activity series is important because if you are dealing with equations, it shows whether a reaction works or not

For example if you have a single replacement equation and the basic outline of the equation is a+bc=ac+b, then you take the two metals that you are switching out and put the first one (a) and look at the activity series, and take the second one (b) and look at the activity series. If "a" is higher up on the series than "b", the reaction works. But if "a" is lower than "b", then you can label the equation NR, or, No Reaction.