How exactly tuned need to be done at all infra-based and application

I always do have a question since I'm not good in tuning, as I can see most of the cloud services are tuned their OS Image like Amazon Linux. I got a question how exactly around the world engineer doing performance tuning at each server? Example, physical server with application or Web installed inside or Virtual server seat inside VMware and install Apache or some application services.
What kind of scenario or there's common profile we actually can use to do it? And also after performance tuned is that any other side possibility impact? Like suddenly happen server down because of tuned or Application intermittent.