Comment by freakynit

If most of your users are concentrated in the same (or nearby) time zones, your traffic can easily vary by 5–10x over a 24-hour period. In that case, 30% average CPU utilization doesn't mean you have 70% headroom at peak... it may already imply you're close to saturation during busy hours.

For example, if 30% is your daily average and your peak-to-average ratio is ~5x, you're effectively hitting 150% of capacity at peak. Obviously the system can't sustain that, so you'll see queueing, latency spikes, or throttling.

The 30% guideline makes sense if you care about strict SLAs and predictable latency under peak load. If you're more tolerant of temporary slowdowns, you could probably run closer to 60–70% average utilization, but you're explicitly trading off peak performance and tail latency to do so.