It’s a game with exploration elements, so the idea is that an areas you’ve visited may only have estimates of what resources are available. In some cases you could be the first person exploring it or noting its qualities.
The in game reason is the survey data you get is asked of you by one of the constellation members, as their space base “The Eye” has scanned all it can. We use the scan data for finding more artifacts (though I’m assuming it doesn’t outright give more missions). You can get the survey data before this activity and sell it for about half, which is why I assume it doesn’t really affect much.
There are also missions that ask for experienced surveyors to look for hospitable planets for their colony.