You use a twist drill bit and only rotary motion when you want to CUT a hole through a material like wood, steel, plastic, aluminum, etc.
You use the hammer function and a masonry bit to BATTER a hole through masonry materials like brick, concrete, rock, mortar, etc.
Consequently, a dull masonary drill bit works much better than a dull twist drill bit cuz there's no cutting involved. It's all a matter of bashing the material in front of the bit into rubble (that gets augered out of the hole by the flutes).
If it wuz me, I wouldn't use the hammering function with a keyless chuck unless you're drilling into masonry with a masonry bit. I have a Hilti rotary hammer with an SDS chuck, and as a freebee I got a keyless chuck accessory that could be installed in the SDS chuck for using twist drill bits up to 1/2 inch in diameter. The owners manual warned me never to use that keyless chuck accessory when the tool was in hammer mode because the keyless chuck was press fit together and the pounding action of the tool could shake it apart. Admittedly, the hammering action of your cordless drill won't be as strong as a corded rotary hammer, but if it wuz my cordless drill, I'd play it safe and not use the hammer function unless you need it (meaning you've got a masonry bit in the keyless chuck and you're drilling into masonry).
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