I know historically P releases have said they should only be installed on advice of NetApp Technical Support, but we really really mean it for D releases.
D releases are for specific BURT fixes, and should only be installed by the customers they are created for, and only on the systems they are intended to fix BURTs for. They are also not typically cumulative - ie, D5 doesn't necessarily contain the fixes from D1-D4. They might, but don't always. So no, don't install D-patch releases 🙂