Stereo > Mono

If I drop a stereo file on to a mono track in Nuendo the L/R wave-forms are still visible on the mono track but the track plays, presumably in mono. How would that differ from converting a stereo file to mono in the Pool?

I’ve tried this with stereo Kick Drum and Hi-Hat recordings and can hear no difference between the original stereo track and the ‘mono’ versions, but can hear a difference if the same thing is done with a Snare recording (the stereo version sounds bigger and more present). Could this be to do with frequencies or the way the drums were recorded?

Probably phase cancellation in various frequencies. For a snare and associated reverberation the frequencies are likely to be more obvious to the ear than those found in the other recordings.