I should imagine the 'down side' is fewer mpg - using more diesel for increased acceleration.
Manufacturers set the ecu to meet emissions tests; give good mpg; give good power - for good read 'acceptable' to the majority of those who are likely to buy the car.
If you improve one of them - the others will suffer - it's the old story you don't get owt for nowt.
The most important thing is that you're happy with the change - that's what really matters. :thumb: