.993 is pretty hard to achieve. That beind said if its a light fruit or a white wine its a good idea to do so as these are pretty easy for the win e to get oxidized, reds I always let ferment to dry in primary, whites I usually rack over at around 1.015 to make sure there is a blanket of gas to protect them.
...racking it early is to get it off the lees to prevent any off flavours developing in the wines.... at times I have fermented to dry in the primary.. then racked off to a secondary and sulphited/sorbated for bulk aging. Depends on how much of a deposit the wine throws.
If it sits in there too long without an airlock and lid sealed then the extar 02 can oxidize it and all the lees can also give it an off flavor so yes there is a point at which it can do harm but you have not reached that point if you had the lid snapped on with an airlock on it.