As far as i know every log message from the application will be performed. but will only be filtered by the loglevels selected by the logging instance. 

The performance impact is minimal. so if a specific logging is performed thousand times a minute, you might consider if this logline is usefull of add a condition surrounding the log action filtering out unwanted logs.

Some performance tools (like APD) also adds a logging instance which will send logging to the apd service. This also decreases performance. 

removing lognodes might not increase performance that much. 

there is one mendix doc describing log performance impact for client actions called: JSON. only set this to DEBUG for a short while when clients are experiencing issues. 
https://docs.mendix.com/refguide/logging/#json