I've put my publication elsewhere (e.g. on a personal/departmental webpage)

Great – can we have access? We can download it and add it to the repository.

Putting it in a repository means it is curated and is a more permanent link and benefits from institutional support. Evidence suggests that the Google ranking of your article will be higher (first page) if it is in a repository – This can be demonstrated fairly easily.

Articles available in an open access format (specifically, in a repository rather than on a static webpage) are likely to be cited more frequently. Logically, this would help drive up citation counts.