You're missing the word "can". It's a very important part of that sentence.
If your software can't even use 80% of one node, it has scaling problems that you need to address ASAP, and probably before throwing more nodes at it.
> It puts more strain on the hardware and will cause it to fail a LOT faster
Unless you're hammering an SSD, how does that happen? CPU and RAM should be at a pretty stable amount of watts anywhere from 'moderate' load and up, which doesn't strain anything or overheat.