You don't add it when you're making or storing the stock. You add it when you're making your sauce. In lots of cases, you're not saucing until the main dish is done and plated.

I am not sure I would use gelatin in a vegetable stock. Things I've used: arrowroot powder, cornstarch, flour, potato starch, agar. A classic veggie gravy would be veggie stock + flour/butter + maybe some tomato paste.

A similar effect for vegetarian dishes would be to add agar - changed the mouth feel.

Typically you’d do this while making the dish, not add it to the stock ahead of time .

A more viscous sauce will adhere to the food it's on better and feels different in your mouth. Most people would describe it as "richer".

You've never heard of using cornstach slurries (sp) to thicken soups? I feel like that's a pretty well known trick for getting the mouth-feel right.

Sorry if I was vague. My question was why you would want your meat stock to have a thickener. I mean I don’t premix all my cornstarch with spices and salt since I want to be able to pick the right amount of aromas and taste separately from how thick I make my soup.

It's more of a mouthfeel thing than a thickener. Gelatin, in the amounts found in a good stock, will still be quite liquid when the stock is at serving temperature, but will sort of coat your mouth with flavor even when the broth hasn't been thickened with a roux or cornstarch.

They were pointing out that with meat stocks it depends what went into the pot - a good home made (or restaurant) one typically already has enough to make it “gel” in the fridge. The box types you mostly get in a store didn’t have this, so might want to add if your recipe assumes it.

Ah, got it - your comment(s) make more sense now for sure.