Inventory Items can reward progression when actions are performed on them. A common example of this in Destiny 1 was Bounties, which would reward Experience on your Character and the like when you completed the bounty.

Note that this maps to a DestinyProgressionMappingDefinition, and *not* a DestinyProgressionDefinition directly. This is apparently so that multiple progressions can be granted progression points/experience at the same time.
Type: object
Object Properties
Mapped to Definition
The hash identifier of the DestinyProgressionMappingDefinition that contains the progressions for which experience should be applied.
Type: uint32
Mapped to Manifest Database Definition: Destiny.Definitions.DestinyProgressionMappingDefinition
The amount of experience to give to each of the mapped progressions.
Type: int32
If true, the game's internal mechanisms to throttle progression should be applied.
Type: boolean