CapEx & Maintenance maximum set-aside?

[Jeff C.]

I understand that, as a buy-and-hold investor, it is important to set aside a certain amount of cash in order to cover maintenance and capital expenditures.

It seems a bit odd, though, that these are typically expressed as a percentage of the gross monthly income. While I understand that may be a sensible saving rate, isn't there some point where one might be safe to stop setting aside funds and be reasonably 'safe'?

Or is there a reason to set aside funds in perpetuity, regardless of how much one has stockpiled?