If I upload a GPX file, how long is it retained? Forever? Or is it eventually deleted? After all that is really lots of data. Especially if some people upload traces for roads that already exist in the database. Is it discouraged to upload gps traces if a road for that trace already exists?
The whole idea of traces in OSM is to have multiple traces of the same road so we can more reliably map it. In lot of already well mapped places this is no longer that important, because of the availability of good aerial imagery. But in the biggest part of the world we don have good images.
So traces are never removed from the database. (At least up till now.)
Also to mention that aerial images sometimes are not aligned correctly to the real world. So GPS-Traces help to check reliability of aerial images and can also be used to correct the offset of aerial images.
agreed with PHerison.