To understand why there can be no answer to this question, you first need to realise that other people are using iNaturalist in a thousand different ways you probably haven’t even thought of.
I might be using the site for building my “life list”, and once I have logged a species once, I may not be interested in ever logging another observation of that species.
My next door neighbour might be making a list of all the species found in his garden, and perhaps he is also interested in seasonality (what birds visit when, what flowers when) so he’ll be logging observations of the same plants and animals on different days.
Down the road, perhaps a school is having a competition for which student can find the most species in the school grounds. That’s could yield hundreds of observations of the same species from the same locality.
A team of botanists at the local university could be working on a theory that the sycamore tree is, in fact two species with subtly different leaves. They would like to have photos of thousands of sycamore trees, as many as possible, regardless of where they are located.
The truth is every observation is valuable to somebody. People here are not merely interested in knowing about each species’ distribution, and filling in gaps in the map, but also when things are seen, and so on. Even making an observation of the same one plant in your garden every week for 10 years would yield very interesting and useful information (for example: why did it flower 6 weeks earlier than usual this year?)