When you pull the trigger on a processing job involving a few hundred GBs of data and get a parameter wrong, you may have to re-run it and pay for the wasted compute/bandwidth. In this sense, getting the coordinate system right is no different than getting any other parameter right.

When you increase bad inputs by 1000x, the magic of scalable cloud infrastructure multiplies your mistakes for you automatically.

If the simple planar distance and the geodetic distance are significantly different and you use the planar distance for some analysis then the best case will be you got your analysis wrong, the worst case would be that you have bought the wrong quantity of material or built some unworkable or unnecessary. Or you just misplace where poles are and work crews waste time finding them, or you give wrong information for call before you dig queries and somebody goes straight through a pipe or conduit.

GIS systems are an area where software and the physical world can meet in ways many devs don’t appreciate.

You discover the error too late and fail to submit your proposal. I've seen this happen for a 7 figure bid. This was in orgs that are not used to coordinate systems, for reference we have thousands of crs in my local area, sure when you know that you need so many you usually have the experience to get it right.