While I agree with Fl1ingfrog that the aural environment is also part of your learning, I am not in favour of switching off ANR or avoiding it for this purpose. ANR only reduces the aural impact of the low frequency noises and there are also many users who will tell you that you can hear more of what your engine is doing thanks to ANR. The cumulative effect of noise on your hearing is a long-term effect and by the time you notice it, you will be too late to do anything about it. Short-term, you will feel less fatigued thanks to ANR and this will be a positive effect, especially during training. Opinions vary on this subject of course.