How often should an editor ask for reviews from the same referee? There is a journal editor who keeps sending me review requests. He sends a new one shortly (a couple of weeks) after I return the previous one. I tend to accept because they align quite well with my expertise and I want to stay in good terms with this editor, who is a prominent figure in the field. I am a slow reviewer, but tend to give quite detailed and comprehensive reviews (compared with what I usually get for my own papers), and I guess the editor is happy with the quality of my reports, otherwise he wouldn't keep asking. However, I wouldn't mind if he asked less often. After all, this is only one journal and I also get review requests from other journals.
I have no experience as editor, and I am wondering if there are any best practices from that side. Is it common for an editor to keep &quot;milking&quot; that reliable reviewer? For those of you who have editorial duties, do you have any limit on how often to ask? Once a month, once every two months?
My intuition tells me there's a risk the reviewer gets tired of getting so many review requests from the same editor and the editor may end up losing that valuable resource.
From my experience as an editor, it is not unusual for referees to ask for &quot;time off&quot; from being assigned reviews and give bounds for the frequency of requests.  As Buffy suggested, some editorial systems allow referees to enter this information and the editor sees it before sending out review invitations.  I was glad to honor such requests from reviewers---I wanted them to feel satisfied &amp; respected so that they would write more helpful reports in the future.
Similar to Fred Douglis, I tried not to ask anyone (other than editorial board members!) to review more than twice a year.  However, we aren't mind readers.  If your pattern is to submit a helpful report and then say yes to another request soon afterwards, then maybe you have the time, really enjoy reviewing, etc.  What editor wouldn't follow up on such enthusiasm?  My advice is that it's up to you to speak up about what you have time for, how often you're comfortable reviewing, etc.  I think there's very little risk of getting on the editor's bad side by setting up those kind of parameters.