I was watching some airport documentary and I noticed that the planes always had to park precisely. I honestly didn't think so much of it before, but in the documentary, an aircraft parked badly because the VDGS couldn't detect it correctly due to fog, so it had to be pushed back to park again with the help of a marshaller.
The only two reasons for this I could come up with are the following:
Jetways: I figured it's because of the jetways, but they can move about so as to adapt to where the plane is. Plus, when parking on stands, the accuracy is the same and there is no jetway.
Aesthetics: I also thought it could be about aesthetics, but the systems used to help the pilot park (a marshaller or VDGS) can be expensive so business-wise, it wouldn't make sense to be so strict on parking if it's just for the looks.