I'm exploring z-scores as a method to spot anomalies in my data. What I don't really understand is what the benefit of using a z-score is over just looking at the percentage difference a value has from the mean average in the data?

For example, if I calculate that a value is 70% different from the mean, isn't that enough to assess if it's an anomaly ? What is the added value to calculate it's z-score?

Thanks for any tips!

Pat