Extending the gear ratio makes sense if the engine performance has been increased by successful tuning measures. With the longer gear ratio, you can convert your extra power into more speed.
In addition, the cylinders and the rest of the engine are protected, as they no longer have to be revved up as much.
In series engines, longer gear ratios are generally not advisable, as in most cases there is not enough power to convert the extra gear ratio into top speed.