This tag first crossed the DWG’s desk in 2016; I guess the proposal followed from that (and was later abandoned). Back in 2016 a person using the tag wrote to the person who had raised the issue with the DWG:
… One of the tags we use internally is “curve_geometry” which allows us to identify nodes that have geometrical importance. The reason this is needed on our end is because we filter nodes that have no navigation tags and, for simplicity and performance issues.
That was basically what I said in back 2016 too 
The worry back in 2016 was that we’d get millions of these tags and a small subset of mappers annoyed when other mappers removed a tag of unknown meaning. That doesn’t seem to have happened; we have 12,000 tagged “curve_geometry=yes”
It doesn’t mean that adding them is a good idea though - hopefully the person adding the tags now can be persuaded to discuss it here.