Theory I had heard was that in the early days the main fuel filter was a paper based product and if left too long could start to break down, hence the need for a mini mesh filter as a last line of defence.
Dunno if that's true or not, but I think most of them left the factory with some sort of pump filter at the banjo, but over the years many have had them removed, either on purpose, or like me, when removing for cleaning/inspection, I dropped it never to see it again!
With a extension on your socket nowt needs to be undo to get the banjo out and go digging for the filter. The tiny basket was a surprisingly long way down inside the pump, to the point I initially would have sworn there wasn't one there. When I finally lost it underneath somewhere, revs jumped up above 3000 without an issue on fast roads and definitely receive a bit more kick out of the old gal as she was getting partially starved of fuel before.