As a map is a two dimensional representation of a three dimensional object, however you represent it must be a distortion. You pick the distortion to minimise errors in the aspect you care about. So the mercator projection was designed to preserve bearing from any point to any destination. That is more important for a sailing ship than preserving sizes of countries. Other projections keep area better but lose the bearing preservation.

You sometimes here people claim one projection is better than another. That's meanless, really. One projection can be better than anothor for a given purpose, not in any absolute sense.

A different, but related question is the point of origin and orientation. The mercator projection has its origin as the intersection of the Greenwich meridian and the equator, But you could pick any other point as the origin. In the middle ages Jerusalem was often picked for maps. There are old maps with China at the focus. I have seen - admittedly tongue in cheek - maps with Australia as the centre and 'south up'. This choice is important for pyschological reasons more than operarional use


Then again, tiles used in SatNavs do not use the same origin for the whole map.

This is surprisingly large subject and one I had some involvement in in the early 1980s.