As is common in the tradition of the zettelkasten, Goutor advises "that each note-card should contain only one item of information, whether a quotation, a summary, or anything else". (p28) He ascribes this requirement to his earlier need for clarity. (cross reference: https://hypothes.is/a/SfWFwENIEe2KfGMbR5n7Qg)

He indicates that while it may seem wasteful to have only one item on each card that the savings in time, efficiency in handling, classification, and retrieval will more than compensate for the small waste.

This sort of small local waste being compensated for by a larger global savings and efficiency can be seen in the design of the shipping container industry as discussed in Mark Levinson's The Box (Princeton University Press, 2008). Was this the exact sort of efficiency mentioned by Ahrens'? (Compare at https://hypothes.is/a/t4i32IXoEeyF2n9jQxu6BA)