from the 2017 manual
Engine
Depending on the profile selected, the engine responds more spontaneously or more in harmony with the movements of the accelerator.
Additionally, when Eco mode is selected, the Start-stop function is automatically activated.
In vehicles with automatic transmission, the gear change points are modified to position them in
lower or higher engine speed ranges.
Additionally, the Eco1) mode activates the Inertia function, enabling consumption to be further reduced.
In manual gearbox vehicles, Eco1) mode causes the gear change recommendation indications that appear on the instrument panel to
vary, facilitating more efficient driving.
Dynamic chassis control (DCC)
DCC continuously adapts the shock absorbers to the condition of the road and current driving conditions, according to the pre-set
programme. In the event of a fault in the DCC, the following message is displayed on the instrument screen Fault: damping setting.
Steering
Power steering becomes more robust in Sport mode to enable a sportier driving style. In the Leon
Cupra the power steering
becomes more robust in
Cupra mode.
Air conditioning
In vehicles with Climatronic, this can operate in eco1) mode, especially restricting fuel consumption.
Adaptive Cruise Control (ACC)2)
According to the active driving profile, the acceleration gradient of the adaptive cruise control varies.
Electronic self-locking differential2)
The self-locking differential adapts its behaviour depending on the driving profile chosen. Normal mode or
Cupra mode can be selected
to prioritise improved traction in sport driving.
I have a map on my car and the mappers say the same thing as Seat eg even in
Cupra mode you can get good MPG. Its all down to your right foot and how long you hold the gear on a manual.
With regards to warranty, not that anybody seems to care (Brokers etc) but you should check your credit agreement to see if mods are allowed (almost certainly not) I have seen one reported case of a car being taken back as the owner had it mapped and it triggered a TD1 Flag and the dealer notified Seat Finance. However in general as stated above nobody seems to care as long as the car is returned how you got it.
Insurance company you need to notify as you have modified the car.
Seat Warranty not an expert but from the stuff I have seen they will refuse warranty if they think your modification could in any way contribute towards the failure. So if you have the usual door rattles, Lights Cracking etc then they are not related so cant see how they could justify saying no but I suspect most would not even notice. As you salesman suggested it in the first place I would ask him.