This script allows you to define "Parameter bonuses" for your actors. A parameter bonus is simply a bonus that will be added to your parameters based on a formula. Bonuses are added on top of base params; if you set your base param to 0, then the bonuses can be used as a custom parameter formula.
For example, suppose you had custom parameters that allowed you to define stats like “strength” or “intelligence”, where str increases your atk and max HP params while int increases magic attack and magic defense stats. You can use parameter bonuses to define formulas that will allow your str and int stats to contribute to the other parameters.
Since the parameter bonus can be any formula, you can define bonuses based on anything.