Depends on the company...
Atlantic Airlines request you do so every six months for instance.
Others don't care and only want one when they say they're recruiting.
Some don't ever want one because they do everything on-line.
My view is that unless something changes in your CV (e.g. another 20 hours) or you think your CV is not on file any longer, don't keep sending them just for the sake of it - it's unlikely to make a difference.