Let me give you a couple of really detailed case example.
I’m a PhD student studying a specific species of Dragonfly, Hemicordulia Tau. It’s a pretty common dragonfly in the parts of Australia where it is found, so I can imagine for a lot of people it might be a ‘record once, then forget’ species.
I study dragonflies I catch in the wild, so i spend a lot of time out catching them. One day I had an idea - I downloaded all the observations of the species from I Naturalist, and correlated it with local time of day and atmospheric conditions, like temperature. I was able to use this to see patterns in when the species was most commonly found, and was able to target the time I spend catching at times they seemed most common based on iNat observations. As a result of this, i was able to halve the time i spend catching for the same amount of dragonflies, giving me more time to read the literature, run my experiments, or have a life beyond the PhD!
Even though it’s a common species, who knows when and how the data will be useful to someone in the future!