The reduction in descent speed close to the ground is not initiated by system programming, but by a condition called “ground effect” where the column of air under the aircraft becomes compressed by the spinning rotor discs. Although the air is roiled by the props there is still a compression effect.
At high descent speed we can blow though that compression layer and have the gear impact the ground hard enough to cause the aircraft to bounce back up, a common occurrence when using Home mode for an automated landing. If we are not prepared for that we encounter the possibility of quickly applying large control inputs only a couple inches from the ground, and if those inputs were too large or incorrect for the condition the next ground arrival could end up a roll over.
Turtle mode is where the close to the ground descent speed reduction is most evident. If you are new to the H, used to systems with more sedate landing characteristics, or without lots of previous RC aircraft history it might benefit to initially descend in Rabbit but switch to Turtle about 10’ above the ground. Be advised that both descent speed and control response is reduced in Turtle mode. Although slower in response and speed it will allow the new flyer more time to plan control inputs for changing conditions.
A reason not to descend from high altitude in Turtle mode is because the descent speed in Turtle is extremely slow. If battery voltage was low at the start of a descent it’s possible to run out of battery before reaching the ground in Turtle.