Brief - feed reading extension for Firefox

Right now there are two ways of limiting retention of items. They can be set globally as well as separately for each feed:

• "Remove downloaded items after __ days"
• "Store no more than __ latest items"

If you were to think of how to limit the amount of stored entries, these are the two most obvious ways that come to mind. And that's exactly what happened - when I decided to implement this capability, I thought of these two methods and I carelessly added them both. Only recently have I realized that I didn't think it through and that ideally a single option should be enough.

It occurred to me that maybe the latter option isn't really needed. In what situation would you absolutely need to set a hard limit? I can imagine a few cases in which a hard limit may be slightly preferable to a time-based one, but they are too subtle to be convincing. I started to think that this option isn't important enough to justify its place in the UI.

However, I may be missing something, hence this topic. Can somebody point out a concrete use case in which the hard limit is needed and a time-based limit isn't appropriate and simply won't cut it?