There's really no point in a 2kW fan heater, given that all have
thermostats.
I can think of two.

Firstly, the output temperature is lower. It is very easy to melt nearby
plastic things accidentally with a 3kW.

Secondly, after the room is up to temperature, I tend to knock the power
rating down to reduce cycling. I prefer the constant noise to one that goes
on and off every five minutes. If half the power of the device is too high,
then this will be less effective as it will continue to cycle rapidly.

Christian.