It wasn't about bandwidth, but long signatures were obnoxious beacuse you had to see them multiple times per day. https://en.wiktionary.org/wiki/McQuary_limit

People whined about bandwidth waste in this category of complaints but I think it wasn't a real problem, just another aspect of an already-disliked long-signature practice: https://books.google.com/books?id=qoc5DQAAQBAJ&pg=PA97#v=one...

It was on the NTK email list (UK-based tech newsletter) in the late 90s / early 2000s - http://www.ntk.net/ - when people had limited bandwidth on their dial-up connections. Possibly more of a principle along the lines of "save the pennies and the pounds look after themselves" but I remember it clearly.