The only benefit of loading soundfont directly into YEM is saving a lot of time -that way we can quickly get an impression of the sound (in sense, is it "interesting" or not). And even then, we should turn settings in YEM to default values -is the only way to "judge" the sample without being affected artificially.
The big downside of using soundfont directly, is huge resulting voice size. Most soundfonds contain sample for each note individually, which we don't really need. In YEM, we can remove samples for keys we don't need, but there's another problem: most soundfonts contain unnecessary long samples (which increases voice size tremendously) -and we can't shorten samples in YEM.
And the third potentially downside is sample rate. The thing is, soundfonts many time contain 48000Hz or higher samples (which again increases voice). If we manually add samples, then YEM only accept 44100Hz samples. However, if we add soundfont, then YEM also accepts higher sample rates.
That is, to get reasonable small voices (without actually reducing the quality), soundfont samples (for notes that we wish to have) must be extracted as wav files and then shortened and resampled. And then we import them into YEM manually.
It's interesting how differently we "judge" the quality of piano voices. I realize, that many prefer "nice sounding" piano voices... regardless of how real piano actually sounds. And I think that's the reason why piano voices in our keyboards sound as they do: they sound "nice", but far from real piano (in my opinion). Most built-in piano voices are over-polished, have too short decay/sustain, lack resonance, etc... and our ears adapted to that and accepted the sound as "piano sound". And when we find a soundfont that has samples sounding closer to real piano, we aren't capable to recognize that (unless we compare it to real piano).
About too short decay/sustain... for example: if we hit (ff) any key in C1 octave and keep it pressed, every real piano has very audible decay/sustain of over 30 seconds. Piano voices in our keyboards however, have max 15sec sustain, where the last third is at such low level that is not even worth mentioning. Some might say, nobody plays single note for that long time. Is true. But decay time affects how loud will a sound be after (for example) only 2, 3,.. 5 seconds -and that is important! This also applies for higher octaves notes, of course. How is that solved in our keyboard? By adding effects (reverb, hall, etc.)... which just isn't the same.
Just sharing my thoughts,
Bogdan
