What are Trickle Vents? Do you need them?

If I take the vent off, what can I fill the holesslot with? Then all you need to do is cover the trickle vent slots :confused: M

Trimvent Select S13 XS13 FOR USE ON VINYL, WOOD, ALUMINUM OR FIBERGLASS WINDOWS Surface mounted vinyl slot ventilator View · Resources

prince88 slot Trimvent Select S13 XS13 FOR USE ON VINYL, WOOD, ALUMINUM OR FIBERGLASS WINDOWS Surface mounted vinyl slot ventilator View · Resources

benchwarmer football girls slot Order Casement Window - Trickle Window Slot Vent Set Inside & Out - 290mm - 2328mm²EA