Usage of `speed` / `change_speed`

Question submitted via Email to @engelben on 07.07.2023 by K&S Projektmanagement GmbH

In OSC2 there are 2 modifiers to determine the speed of an actor (e.g. a vehicle):

speed ()
change_speed ()  

Both seem to do the same thing (excerpts from the OSC2 spec below).

speed(speed: speed
[, direction: lon_lat]
[, <standard-movement-parameters>])

vs

change_speed(speed: speed
[, <standard-movement-parameters>])

Is there a difference or when can/should one use the modifiers in a scenario?