Exactly.Senkos have a tendancy to be thrown real easy fighting a fish and sometimes even casting if your not careful about rehooking alot.Another common thing is for it to run up the line and be cut like butter.With an o- ring or an alterative like I mention,or several others,the ring fits snug,and is slid onto the worm to usually the center or the smooth segment of the worm and the hook is slid between the ring and worm,so the worm is never even hooked,therefore stay in the game for several fish rather than one fish.A twenty fish day on senkos can end up costing around.....well 6 bucks for every 7 or 8 worms.....alot on a budget.My personal record with the rings is two and a half outings with easily 20 something fish on one worm,and when I replaced it it was shredded from teeth,not a single jump or head shake...that i can handle
on a side note IMO the more pricey,closer to hand poured the senko,the softer,more likely to rip,they are.