I had a similar idea, but Pluck/Bug Bite/Teatime throw a spanner in the works (as does Gluttony, to a lesser extent)
Darn, I forgot about those.
Well, in that case I guess the berries are just effective all the time and genuinely only eaten in need. After all, the item is kept in-game until that point, and obviously can go unused if the holder is knocked out. The same goes for the type-resist berries - it's a slightly weird image for a Pokemon to see an incoming Ice Beam and quickly eat a Yache Berry in the 0.3 seconds before the move hits them, but that does seem to be how it works based on game mechanics. The Enigma Berry only restores health
after being hit with a super-effective attack, too, which makes it rather disappointingly worthless since a super-effective attack is quite often likely to simply knock you out - and even if the attack only does 90% and you survive it, gaining back 25% isn't going to save you from the next hit.
I guess it's kind of like Popeye eating his spinach, but the issue is that that only works for some of the Berries and not others. You can see why a Pokemon would retain a potential Speed or Attack boost in reserve as a last resort. But a Defence or Special Defence boost is most useful when applied at the
start of battle, not the end, since a +1 boost to your Defence isn't likely to save you when you've only got 10% of your HP left.
This is another one where the Adventures manga presents an interesting contrast. When Emerald's Sceptile fights Noland's Glalie, they grapple and Glalie steadily depletes Sceptile's HP - then the watching Frontier Brains notice that Sceptile is desperately cramming its mouth with Leftovers to try and regain health, which doesn't really fit the way that item is designed to work as far as I'm concerned. Leftovers is supposed to be a gradual, passive restoration, not an "oh crap I'm about to faint, better quickly heal myself up" item to be used in a pinch. One of the pinch berries would have been a much more apt choice in that scene.
(Side note: probably the wrong forum to ask, but what happened to Smogon's item analyses? Time was you could go to a page like
https://www.smogon.com/dex/dp/items/ganlon-berry/ and there'd be a little section detailing how generally useful the item was, and what sort of strategies would utilise it. I liked those.)
That is why my family's farm is all natural grass fed cows.
And let me tell you: you can taste the difference. Nothing beats a steak from a grass fed cow. Unlike it is a Tauros filet mignon.
I'm all about Guernsey cream milk, that stuff is just phenomenal.