When you apply EQ to music composition it will become louder/quiter depending on EQ settings. If music composition was normalized in music studio and you applied EQ to it and let's say increased some Low-Band then most probably truncation of audio samples will occur as a result of amplification. Audio truncation will damage the quality of audio because some parts of audio waves will be cut out. In this situation you needed to use Preamp slider to minimize gain a bit to avoid audio wave truncation. 

Now, Normalize, if applied to music file, will analyze audio of the whole music composition and pre-calculate Master gain (of final mixer) which will guarantee that audio wave will use all output bits. The Preamp gain will be automatically fixed at 0.0 dB level. 

So, manual work with Preamp is avoided and you will get re-mastered audio track after EQ, just like in studio for production. Also as a bonus Normalizer will evaluate DC Offset and correct it. Some advanced audio DACs do DC Offset correction but some DACs may not, so with Normalizer in Neutron it does not matter already. DC Offset will increase quality of audio but in most cases it is almost correct. 

When Normalized track is playing you will notice:

1. Red icon R/G with master gain applied.
2. EQ bands will ignore changes and labels will look red.
3. Peamp and Master sliders will also be red and unchangeable, so you will have only hardware gain slider active.