Why in Linux the sleep timer default is "as host" ?

Thanks for reading my topic.
RPCS3 in configuration "Sleep Timers Accuracy" have "as host" and "usleep only".
RPCS3 Linux version the default is "as host" and the windows version is "usleep only".
Why in Linux the default is "as host" ?
"usleep only" is similar as the console ?
"as host" is usleep only plus timer from host OS or only use timer from host OS ?

What is the optimized option for Linux ? "usleep only" ?