Plug and play tuning BOX:
What it does is, informs the computer that cold air is flowing in. and ECu is fooled to take more air, and more fuel is mixed. Which ends up with taking in more hot air(which is not good).
I would strongly recommend a remap, if it is done by right guys. Because, this controls everything in cars engine bay. From air intake, turbo timing and fuel air mixture. Everything is specified for each conditions. ( % of throttle vs the RPM). All possibilities are covered to give optimal performance. There by increasing HP and fuel consumption without affecting the parts much.
Why dont the company provide the car already remapped?
Simply because everyone out there are not enthusiasts like us. So they give importance to driveability in all conditions. Giving low end torque and mid end torque. While remapped units might be delivering mid to high end torque. The turbo kick is enjoyed by the enthusiasts not by regular drivers. And keeping the HP low also gives less strains to parts which might result in a more efficient car. But at the end of the day, when you rev a non remapped car to say 5000 rpm and a remapped one to 5000rpm. The remapped one will handle it better.(im talking about diesel if you find 5000 rpm to be too less
IMPORTANT: In non turbo cars , these are practically useless.