help me to understand when a tiny #9 roller tip is needed?

[Patudo]

As to your suggestion on trying fly fishing for bonito or skipjack with someone using lighter leader, I have actually done this  (yellowfin too). 

My suggestion was to try fly fishing (or whatever style you fancy) with hi-vis straight to your lure or hook.  I'd genuinely like to see what results an experienced fisherman gets doing this.