I get the feeling it's largely vestigial, like an appendix. The only thing I ever use the entry key for is when typing titles in on successive mp3s e.g. enter, type in the name, enter, arrow up, enter ...

On modern Japanese keyboards, it's common for the Enter key to be located on the far right. However, in the early days of typewriters, there was no such key. Marcin Wichary has summarized the history ...