Answer by Julian for When to use a Class vs. Function in PHP

Using classes is a good way for grouping your functions.

The difference lies in the usage of the programming paradigm. Classes are necessary in O.O.P. but are not necessary in the Procedural paradigm. In the Procedural paradigm you can group functions in a file, which can be seen as a module.

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You could use procedural paradigm. Classes are not really needed in this paradigm.

function miniCal($string_1, $string_2){
//do something   
}

//invoke function
miniCal('arrayVars1', 'var2');

You could use OOP paradigm. Classes are needed.

class Calculation {

public static function miniCal($string_1, $string_2){
    //do something   
    }
}

//invoke function
Calculation::miniCal('arrayVars1', 'var2');

Conclusion

Both paradigma's work, but the OOP example from the above is using a Calculations object which contains all calculations methods (functions). The Calculations object groups calculation functions, thus keeping them in one place.

The O.O.P. paradigm in this example obeys to a principles called "Solid responsibility". The idea behind this is to keep the code elegant, maintainable and readable.