Make sure backup arrangements work in real operating conditions — not just on paper.
Assess whether backup arrangements and repair access are sufficient under real operating conditions, not just on paper.
Many redundancies look adequate in design but fail in practice because of shared utilities, common-cause failures, or inaccessible maintenance points.
When reviewing critical systems, plant layouts, or support philosophies.
PI assesses backup logic, repairability, and concurrent maintainability implications — the things drawings alone don't reveal.