For me, there's no moral reason to finish a single player game. The player is his only judge.
From a gaming POV, these are some items to consider:
- a bad game may have a temporary impact on the average but no negative impact on tiering up,
- a bad game finished provides experience at the last holes, XPs, and an inner support not to have given up too soon,
- consider the time it takes to finish.
For the last man standing in a multiplayer game, add the completion %% as a further item. AFAIK, it will be counted in regardless.