Just yesterday....doing some training here in the UK...in the Huey...lowering the collective much at all after touchdown on the sod brought you to an almost instant stop...thus much stress on the skid crosstubes and mounts...and a very real risk of poking the nose into the ground.
We found we had to carry a bit of collective to prevent that...but as Nick says....lowering the collective as soon and as much as possible is the desired technique. The amount and rate of reduction depends upon how "sticky" the surface is.
On a smooth hard surface...a smooth, gradual reduction of collective will bring you to a stop in a much shorter distance than merely holding what pitch setting you have at touch down. The key is to avoid causing the aircraft to pitch, buck, or stop abruptly.