Resampling is the process of audio data conversion from one frequency to another. Modern mobile devices normally support 48000 Hz audio frequency and most music files have 44100 Hz frequency. 44100 Hz is the standard frequency of the CD, thus it is that widely used for the music files. To play music file on a 48000 Hz device we must convert its frequency to the frequency of the device, it is called - Resampling.
Neutron is using high-quality high-precision resampling algorithm which does not alter frequencies and quality of the music (tested) and thus you really do not need to worry about the resampling process, it happens transparently for you.
If your device supports Hi-Res Audio, e.g. offers more than single frequency (you can see it in Audio Hardware -> Frequency settings) then you could activate Audio Hardware -> Follow Source Frequency option which instructs Neutron to set device frequency to the frequency of the playing file, in this case no resampling will happen and you can achieve bit-perfect playback.
Hi-Res Audio support make it possible to benefit from Oversampling technique by activating Audio Hardware -> Oversampling and setting the desired oversampling ratio. The higher the ratio, the higher the oversampling frequency. Oversampling technique improves the precision of audio data processing in case you are using some of the provided DSP (Equalizer, Crossfeed, Compressor, ...). Many modern DACs oversample audio data internally in its hardware but Neutron can do it earlier and you will benefit from a higher precision of audio data processing (DSP).