Low-frequency slots pay more often but in smaller sums. The point is in the way these slots realize their RTPs. With more volatile slots, you can expect the realization of the RTP through big wins and bonus features.  In contrast, the less volatile slots will replenish your bankroll and fulfill the RTP little by little. This is why slots have paytables and Random Number Generators that give a structure to the slot game online and a chance for players to win even on a short-term basis.