When would you enable Person Accounts, and what would you warn the customer about?

Person Accounts are strongly recommended for customers using Fundraising or Program Management, and I would enable them for a typical donor-and-participant organisation. But I treat it as an architectural decision that gets written down.

1. The warning that matters most: enabling Person Accounts cannot be undone. There is no disable switch, no support reversal, no record-count exemption. Any trialling happens in a sandbox or developer org.
2. The second warning: Person Accounts are not supported with the Nonprofit Success Pack. If the org runs NPSP, this is not a decision to make in isolation.
3. The case where I would not enable them is a grantmaker funding mostly organisations. Person Accounts are not required for Grantmaking, and a foundation with a named contact at each grantee is generally better served by the Contact plus business Account model.
4. Even then I document the decision and its implications, because if Fundraising is added in phase two, the constituent model becomes a migration question rather than a configuration one.