Data minimisation is the principle that you should collect, use, and keep only the personal data you actually need for a clearly defined purpose. It is the opposite of “collect it now, maybe it will be useful later,” and it treats unnecessary data as a liability rather than an asset - ico.org.uk 
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In UK GDPR and EU GDPR, data minimisation is framed as: adequate, relevant and limited to what is necessary. for the purpose you said you were pursuing. The important word is “necessary,” because it forces you to justify each data field, each data flow, and each retention period, rather than drifting into surveillance by default - legislation.gov.uk
Data minimisation is not just a compliance slogan. It is a security and governance design strategy: the less sensitive data you collect and centralise, the less you can leak, lose, be compelled to hand over, or be tempted to repurpose. Minimisation shrinks the “attack surface” of an institution and also shrinks the scope for internal misuse.
In deliberative governance, minimisation matters because participation often requires safety. A Citizen Assembly process may care about demographic balance, but it does not automatically follow that organisers should hold raw, identifying spreadsheets of health status, sexuality, disability, or neuroatypical cognitive style. A minimising approach asks a sharper question: what is the smallest proof the process needs in order to be fair, and can we avoid storing the underlying sensitive attributes at all.
Modern privacy tech makes this practical. With Self-Sovereign Identity and Verifiable Credential, people can hold credentials on their own devices rather than feeding a central database. With Selective Disclosure and Zero-Knowledge Proof, a participant can prove “I fit this category” or “I am eligible” without revealing the underlying private fact, which is often the only part that actually creates harm if leaked or weaponised.
Data minimisation also includes time. Even if you truly need a piece of personal data, you should keep it only for as long as the purpose requires, and then delete or irreversibly de-identify it. Otherwise “temporary” collection quietly turns into permanent archives, and permanent archives quietly turn into permanent power - ico.org.uk
A simple cultural test for minimisation is whether you can point at each data item and say: “If we did not collect this, the purpose would fail.” If the honest answer is “it would be convenient,” that is usually a minimisation failure, and it is often the first step toward the Transparency vs Safety trap.
Also see: - Minimal Computing - Digital Minimalism