It all boils down to your setup. Unix socket should be preferred for localhost, since you’re theoretically adding an overhead if you pick TCP. OTOH, the overhead with TCP should be negligible and the configuration could be more portable. @eva2000 may have further specific insights
Well yes; according to PHP docs definition of emergency_restart_threshold,
If this number of child processes exit with SIGSEGV or SIGBUS within the time interval set by
emergency_restart_interval, then FPM will restart.