Online Tool Store
· 4 min read
How to Stop Collecting Data You Don't Need
Manesh Jayawardhana
CIO & Co-founder
The signup form asks for date of birth. Nobody remembers why. It was added in 2019, possibly for an age check that was never implemented, and it has been collected from every user since.
That field is now something you store, secure, back up, include in every subject access request, and have to explain if you are ever asked what it is for.
The question that does the work
For every field: what specific thing do we do with this?
Not “it might be useful”. Not “marketing wanted it”. A concrete use — a feature that reads it, a report that groups by it, a legal requirement that mandates it.
Fields that survive that question are fields worth collecting. Fields that do not have an answer are pure cost, and there are always more of them than anyone expects.
Running this on a form of fifteen fields typically eliminates three or four. Running it on a database schema that has accumulated for a decade eliminates more.
What each field actually costs
Collecting a field is not free once, it is expensive continuously:
Storage and backup, which is trivial per field and non-trivial across systems and retention periods.
Security scope. Every field is something that can leak. A breach involving dates of birth is a materially worse breach than one without.
Subject access requests. Everything held must be found and disclosed, across every system it reached.
Retention obligations. Data held must have a retention period and a deletion process, and both need building.
Conversion cost. On a form, every field reduces completion. A field nobody uses is costing signups to collect nothing.
| Field | Has a stated use? | Verdict |
|---|---|---|
| Account access | Keep | |
| Date of birth | None found | Remove |
| Phone | Used by support | Keep, if support actually calls |
| Company size | Marketing “might segment” | Remove |
Minimisation is a legal principle as well as good practice
GDPR and most modern privacy regimes require personal data to be adequate, relevant and limited to what is necessary for the purpose it was collected for. That is the storage limitation and minimisation principle, and it is enforceable.
The practical version is simpler than the legal one: data you never collected cannot leak, cannot be subpoenaed, does not need a retention rule, and does not appear in a disclosure request. Deleting a field removes work in four directions at once.
This is not legal advice, and which fields you may lawfully collect depends on your jurisdiction, sector and basis for processing. But the direction — collect less — is both the legal expectation and the engineering one.
Audit the third parties too
The fields your own systems hold are the visible half.
Analytics, support desks, email platforms, payment providers, session recording tools and advertising pixels each collect their own data, hold it under their own retention rules, and frequently in another jurisdiction.
A minimisation exercise covering only your database misses most of the actual exposure. Session recording in particular can capture form contents including fields you deliberately do not store, which is a common and unintentional collection.
The practical step is listing every third party receiving data, what each one gets, and whether that is necessary. Removing a tag that nobody has looked at in two years is the cheapest privacy improvement available.
Common mistakes to avoid
- Keeping a field because removing it feels risky, when the risk runs the other way.
- Auditing the form and not the database, which holds fields the form stopped sending years ago.
- Collecting “for future analysis” that has no defined analysis.
- Forgetting third-party tools — analytics, support and marketing platforms hold their own copies with their own retention.
- Removing a field from the form and leaving the column populated with historical data nobody reviewed.
How to do it with Data Minimization Auditor
The Data Minimization Auditor walks each field against a stated purpose.
- List every field the form or table collects, including the ones nobody questions.
- State the single purpose the collection serves.
- Remove the fields with no answer — and remove the stored historical values too, not just the input.
- Have anything involving special category data reviewed by someone who knows your jurisdiction.
Your national data protection authority publishes guidance on minimisation. Other privacy tools are in the tools directory.
Frequently asked questions
What is data minimisation?
The principle that you collect only what is adequate, relevant and necessary for a stated purpose. It appears in GDPR and most modern privacy regimes, and it is also straightforwardly good engineering.
Why does collecting less help?
Data you never collected cannot leak, does not need a retention rule, does not appear in a subject access request, and does not have to be secured. One deletion removes work in several directions.
Is this legal advice?
No. It is a structured way to review fields against a purpose. Which fields are lawful to collect depends on your jurisdiction, sector and processing basis, and needs qualified advice.
Final thought
Ask what each field is for and write the answer down. The fields where nobody can finish the sentence are the audit’s whole output.