As I have military pilots in my family I thought I'd ask one who has flown many helicopters in combat and S&R situations. Here is what he told me:
In normal forward flight, the disc is slanted forward, so some/majority of the thrust is downwards, but some is backwards to counteract drag or accelerate. When you decide to slow, the disc is tilted backwards so now some of the thrust is forwards.
What also happens is that the relative airflow that was impinging on the top of the disc in forward flight is now impinging on the bottom of the disc as you decelerate.
In forward flight this flow is a thrust penalty because it means that the change in downward flow through the disc by the rotor blades is more limited. I.e., the air is already flowing down and the rotor blades find it harder and harder to shove it any faster. They would need to rotate faster and faster to get any lift and then hit supersonic compressibility problems. (This is why modern blades tend to be funny shaped like Lynx/Merlin etc.)
Same problem propellers have on fixed wing. There is a speed at which they just can't propel the aircraft any faster.
Conversely, when the disc is tilted back to flare, the airflow is all bonus. It is known the rotary aviation as the green arrow and what allows autorotation.
I have zoom climbed hundreds of feet upwards whilst assaulting targets in full autorotation with the collective lever full down and essentially nor requiring engines at all.
The upshot of this is that as you transition from normal forward flight by tilting the disc back you need to lower the collective to maintain level flight or you will zoom climb.
However, you don't get something for nothing. You are trading the forward energy of the whole helicopter for rotational energy in the head.
Eventually you slow to a stop, and at this point you require engines to sustain the rotation of your rotor system, and if you have maintained a lot of nose up it is a very significant amount of power.
The power required curve for helicopters is a U shape with most power being required at hover and max speed and min at about 70kt in most helicopters.
The upshot of this is as your speed tapers off you need to steadily lower the nose or can get bitten hard by the power requirement when the forward momentum ceases especially if you are flying an underpowered toy which almost all hobby helicopters are.
This thrust deficit is exacerbated if the nose is held high because not all the thrust is supporting lift, some is accelerating you backwards.
This is an example. The pilot is coming in too hot and holds the nose very high until a very late stage. He then let's a rate of descent build and doesn't have time to arrest before hitting the ground. Hovering out of ground effect, even military aircraft don't have a lot of spare power, so it is important to correctly judge yeeha flying maneuvers and throw them away before the hover if screwing up. These guys should have thrown it away at about the moment the video starts. I have a feeling that they are approaching downwind as well which makes it all twice as bad.
This is it done properly.
He simultaneously pitches the nose up and enters auto.
You can see the relative aspect of the disc to the airflow switch from slightly downwards to very much up through the disc.
As the speed bleeds off he is progressively raising the lever to maintain height as he runs out of forward energy, then as he approaches the hover he pitches back nose down.