This comes in handy when one is using the Supertrend value as a stoploss level. For instance, one would like to have a maximum stop loss level of 8%. Instead of calculating how much percent the price is away from the Supertrend, one can look at the percent label & make an informed decision as to whether initiating a position would have favourable risk/reward or not.
Another utility would be selling into strength when one is using the Supertrend as a trailing stop loss. For instance, if the price is a certain percentage far away from the Supertrend, one may conclude that the price is now extended & either price correction or time correction would ensue, & decide to sell into strength.
In true TradingView spirit, the author of this script has published it open-source, so traders can understand and verify it. Cheers to the author! You may use it for free, but reuse of this code in a publication is governed by House Rules. You can favorite it to use it on a chart.