Query settings in config-custom.properties

Hello Community,

following config-custom.properties setting is offered:
# Query Settings
# --------------
# Maximum number of threads used in a query. To use an unbounded pool, use the value “-1”. By default, 30 threads are used.
# query.parallel.maxthreads=30

How is this setting influencing
a) end user (frontend) performance?
b) backend ressource consumption?

Is there a best practice about how to configure this setting?

Best regards
Sebastian