If your breakers are tripping at 80% of their rating, something is wrong with them.
On a dedicated circuit, yes. If you’re plugging in something that will consume 80% of the circuit’s rated amperage on a non-dedicated circuit, between swing voltages and any fluctuations, it’ll pop real quick.
I worked in datacenters for 10 years. We kept everything below 80% on our 30A circuits. If we ever lost a redundant circuit, the swing voltage alone on a dual-PSU server or storage device would put a live circuit near capacity before stabilization on a fully-populated rack.