51Did (51Degrees Identifier) and PMP (Preference Management Platform) are derived signals downstream systems can act on without seeing the raw inputs.

51Did - signed identifier (a base64 OWID envelope) carrying a probabilistic value, derived from three inputs: the Device ID (a Hardware-Platform-Browser-IsCrawler tuple produced by Device Detection), the client IP, and the usage purpose (non-marketing, standard, or personalized) declared per request. See 51Did (51Degrees Identifier) for the identifier-versus-value distinction.
PMP - embeddable widget that captures a marketing preference (non-marketing, standard or personalized) suitable as id.usage input to 51Did.

Flow🔗

User → PMP → preference → id.usage → 51Did → downstream

Use one without the other when🔗

PMP alone - you need to collect a user marketing preference and act on it directly (e.g. gate ad personalization, drive a paywall), without feeding it into 51Did.
51Did alone - id.usage=non-marketing (e.g. fraud or suspicious activity), where the preference is set by the integrator rather than the user.

See 51Did (51Degrees Identifier) and PMP (Preference Management Platform). 51Did depends on Device Detection Overview.