i did a driving day with seat and it involved skid pan work, it included driving with the esp system on and off.
I would advise to leave it on unless you are intending having some fun. The electronic systems allow you to keep control of the car even on ice.
We did several tests breaking, accelerating and lane changing.
1) 40 mph heavy breaking on black ice
With ESP, car came to a stop under control within the dvla stated stopping distance.
with ESP off, car came to a stop but it was a bit out of control.
Remember even though esp is off brake distribution with abs is still on.
2) 70 mph lane change
with esp on, the car change lane under control, took a while to grip but it did it, realitivle smoothly
with esp off car just drove forward, understerring like a bugger then when it finally grips your saw the wheel back and can quickly get into a tank slapper situation, not very nice
3) We parked the car 90 degrees to the skid road as though we where at a junction. We where going to turn hard left and nail the gas as though we where pulling out on to a road
with ESP the wheels span and the traction control and stability control allowed the car to turn and pull away, very impressive
with esp traction control of, we set of wheels spinning stright across the road into the imaginary ditch.
We did all sorts of driving and i was impressed with how the electronics would
help in normal motoring situations.
But as i said above, if you are a good drive then you can turn it off. But if you are not that skilled then the electronics packages are a safety net ready to catch you if you go a little to far.
sorry i have gone on a bit, hope this
help