tl;dr: fishing in grana is inefficient for money making and other places will net a higher profit albeit not in safe zones
Full Disclosure: I stand to benefit greatly from people leaving Grana.
If you're fishing in Grana, you're probably doing so because you've heard there's a 200k fish that bites about the same rate as a regular yellow; this is correct.
But if you're AFK fishing, Grana is probably one of the worst places to do so. The problem with Grana is that it is – and please pardon this fishing pun – a bait and switch. People see this 200k fish (Golden Sinipecra) and think that this is the be-all-end-all of fishing spots.
Let me explain to you why it's not:
1. Grana has an atrocious Ancient Relic Shard drop rate
You see, with the implementation of a 200k fish biting like a common yellow, there had to be a balance somewhere. That balance comes to Grana in the form of a relic drop rate probably the worst I've ever seen in any table since I started playing.
After about 11 hours of AFK fishing, my inventory was nearly full. Three of those slots were taken up by relics. Three – (3) – as in
<more than> 2 but
>less than< 4.
Fishing in part 1 of Kama prior to part 2's release, I would come home to approximately 14-17 relics from about the same time. Especially now when relics are selling for over 1m, you're taking a loss to any profit by fishing in this pool.
2. Golden Sinipercas aren't worth nearly as much relics
This sounds like the point above, but it's not. As aforementioned, relics are selling at approximately 1m on NA. Without a Value Pack, I net about 650k per relic.
To match this, I have to catch around 3 Golden Sinipercas.
Despite whatever you may have been told, Golden Sinipercas bite more often but not as often as the other yellows in the table (Spotted Barbel & Miho Spine Loach). After about 11 hours of AFK fishing, I caught 7 of them, which equals out to about 2 1/3 relics.
3. Golden Sinipercas lose freshness (read: profit) while relics do not
This is pretty self-explanatory: The longer you're afk, the less your catch is worth. Your profit is literally depreciating in your inventory. Relics – obviously – do not have this issue.
4. Resources: exhausted
Another self-explanatory section. It's going to take longer for your inventory to fill up than it will at another table. Bite time is awful, but at least it's safe.
5. Imperial Trader will always be low.
With the influx of people comes the dumpage on the Imperial Trader. Most of your profit from fishing in Grana
will come from trading your fish. Imperial Trader has been, and will continue to be, slammed until further notice.
Since exhausted, I net about 1m from Imperial Trader, with the remainder of my profit coming from the regular Trade Manager, and less than 5 relics I've sent to Marketplace.
6. You're away from everything.
Grana is pretty remote. If you're fishing on an alt, you're probably doing it for relics, which can be collected from any marketplace.
As stated above, most of your profit will not come from relics, but from Imperial Trader & Trade Manager, which goes on your character, which you'll have to put in storage, which you'll have to move yourself (or transport) if that character isn't the breadwinner of your account.
Now to answer the question:
Why and how do you benefit from people leaving Grana?
Financially, Imperial Trading will net me more profit the less people are here to use it.
Functionally, I'm hunting the Golden Siniperca title
Golden. It's really all I care about and, once I have it, I'm gone from Grana unless something is introduced for Granges D'Or. This is accomplished easier by a faster bite rate, which – as described above – Grana does not have.
I've fished in Grana since it's release Wednesday
I weathered the DCs and weird you-didn't-get-disconnected-but-you're-sent-to-the-loading-screen-and-not-fishing-any-more. I fished when it was Abundant to Average to Not Enough to exhausted.
If you don't believe me, think I'm lying to you for my own benefit, that's fine. I do benefit from people's exodus of Grana.
I also encourage you to fish in Grana and see for yourself how much silver you're missing out on; although, I would advise you heed my warning that you will be missing out on a lot of silver. Many fishers have done tests at this table and can confirm what I'm alleging: relic drop rate is shit here.