N+ redundancy means you have one more unit than you need. If your load requires servers, you deploy . When one fails, the remaining handle the load.
This works well when failure is rare and one spare is enough. The assumption: you will repair the failed unit before another fails.
N+ is cost-effective but risky under heavy failure rates. If you lose units before repair, you are underprovisioned. For most non-critical systems, N+ provides good balance between cost and resilience.