It depends on a few things. How much rock and sand does your soil have in it. How many birds and size of the run. Do you use litter or anything in the run to block them from getting to the soil and grit in it. Do you live in an area that does not have any rock in the soil? Swamp muck comes to mind but areas of loess deposit or other such areas could also be barren of rock.
Chickens will dig around in dirt to get what they can out of it for grit or any possible nutrients. It is possible for your chickens to get all the grit they need from the soil but it is also possible they could not get enough, especially if they are restricted to a small area, the ground is not very rocky to begin with, and they have found most of the available grit. We all have different circumstances.
I gather small rock, up to the size of a pea, from my gravel road and gravel drive and throw it into the run just to give them plenty of easy access to grit. If your roads are salted for ice, you probably don't want to do this as the salt is not good for them.
I don't know which post you were looking at or the context. It could have been one of mine. Maybe the context was chicks in a brooder? The right way to say it is that they need grit if they have anything other than chicken starter, not necessarily that you have to give it to them.
I just saw that others have posted while I was typing. I agree with them.