Why? Because this chip had seven fully programmable, high grade ADPCM sampler channels (and one of those was an ultra-high grade 55kHz sampler). It still retains the PSG, but in most games, it wasn't used for music.
The chip was most famously used in the Neo Geo AES/MVS, and certain Taito arcade games of the era (such as Liquid Kids).
In the early days of the Neo Geo, FM and PCM were used about equally for music, and the samples, while bigger, and noticeably better than SNES samples, were still mostly in that basic league, so the Neo Geo early games essentially sounded like a duet between a Genesis and an SNES - a really cool sound scheme.
However, later games tried to compete with CD-Rom, and so FM was marginalized, and heeeuuuuge samples replaced relatively small ones. It ended up sounding more like CD-Rom than SNES or Genesis. While I suppose this is technically "better", in my opinion, all it does is rob the system of its magic, especially considering it still ultimately falls a bit short of its new target. So I definitely prefer the earlier school of thought to approaching the OPNB.
I will share an example of each. Magician Lord was a very early MVS/AES game (1990), used very small PCM samples, and each track was about an equal number and prominence of FM and PCM voices. Metal Slug 3 came out a full ten years later (2000), and represents the opposite extreme. A fair amount of the bass is FM, but essentially EVERYTHING else is PCM (using HUGE PCM samples), and even what is FM is so buried under PCM that you really have to strain to even tell it's FM. They represent opposite extremes of the AES/MVS sound.
Metal Slug 3
I have a few other examples of the OPNB as used in the Neo Geo AES/MVS. Here's one that goes so far in the "CD-Rom-like" direction that it's hard to tell apart from its actual CD-Rom (CD-Audio-remix) version - which I will also share for comparison purposes. Then I'll share another track or two that lean strongly towards the "SNES/Genesis Duet" approach. I'll share one that meets them in the middle (a lot of FM, but big PCM samples). I'll share a couple tracks that use PSG (one prominently), then I'll share a couple instances of the OPNBs use outside the Neo Geo (namely, Taito Arcade games).
Here's the AES track that's so "CD-Sounding" that it's hard to tell apart from the CD version - Duck King's Theme from Fatal Fury Special
...and the Neo Geo CD (CD Audio Remix) version - just to prove they're not one and the same! NOTE: the in-game CD-Rom version does NOT feature the super annoying guy shouting over the track (I should know. It's one of only two games I actually own for the Neo Geo CD). Why they added the voice to whatever they pulled these videos from is a mystery...and a crime, because without them, it's my favorite version of the track.
Here's a track that's VERY far into the "SNES/Genesis duet" vibe - In Game 1 from Top Player's Golf
And another - from Cyber-Lip
Here's an example of meeting those two schools in the middle - it is still a PCM/FM duet with FM just as prominent as PCM (in fact, there's even a PCM/FM call and respond). However, the samples are much bigger and better. This is Stage 4 from Last Resort
And one more of those "middle-of-the-roaders" - Super Sidekicks Team Select
Here's a track that uses the PSG pretty prominently - Stage 1 from Viewpoint - an SNES/Genesis duet style number with the PSG front and center - in fact, the track opens with nothing but big sampled percussion...and PSG...
And last for our Neo Geo examples: a "CD-Rom wannabe" style track with the PSG barely noticeable. If you listen VERY carefully at the 1:12 mark, you'll hear very faint square wave drones...that's the PSG.
Now, let's step away from the Neo Geo...but before we step away from the OPNB, I want to share three last tracks all from Taito Arcade games to use the chip. The first one is a well-loved, very "Tomita Arabesque #1-esque" track from Liquid Kids (aka Mizubaku Daiboken) - Stage 2
Here's an unused track from Mega Blast
And lastly, the Stage 1 theme from Growl (which even features a brief cameo from the PSG at 0:55)
And that, friends, is the YM2610 OPNB!
An interesting side note: six of the seven sampler channels on paper, are technically INFERIOR to the sampler channels on the SPC700 SNES sampler chip - however, OPNB shows how ROM and RAM starved the otherwise awesome SPC700 was as despite being "technically superior" (32kHz capable, 16-bit output vs 18.5kHz max, 12-bit output), the samples on the Neo Geo ALWAYS sounded better...and usually WAAAY better....a chain is only as strong as its weakest link - and that's the unfortunate thing about the SNES in many ways.