It is common practice - at least in mathematics - to refer to people one cites in the paper simply by a surname. Hence, one could see sentences like "This awesome theorem is due to Smith.".
However, occasionally the initial is added, and so the above might turn into "This awesome theorem is due to J. Smith". The obvious reason might be that there is also a A. Smith who could be mixed up with J. Smith, but the phenomenon also occurs for people with unique surnames (within the field). Why? (In particular: When should I add the initial, if ever?)