Log Level. For ESXi/ESX 4.0 and later, the default log level is verbose
. For ESXi/ESX 3.5 and earlier, the default level is info
.
I have seen almost every environment is running with default option which does not create any performance issues much. However, reducing it can be done but during analysis it may not give enough information to find the cause of the issue. I would suggest to leave it as default option.
for vcenter its different default is info , when you increase it to verbose you may see some performance lag in vc however it depends on the overall load on VC.