If a tau.conf file is created, then code that uses that TAU lib will effected by the settings in tau.conf. For example, if a directory tau-2.21/tau_system_defaults is created and a tau.conf file is placed in it, TAU will read that file before doing the measurements. A user of that TAU libs can choose to override the contents of that file by placing a tau.conf in their own directory. But by default, if the sysadmin chooses to create this dir, all the users of the TAU libs will be globally affected by this tau.conf.
For example, tau.conf could be:
% cat tau.conf TAU_LOG_PATH=/soft/apps/tau/logs PROFILEDIR=$TAU_LOG_DIR TAU_PROFILE_FORMAT=merged TAU_SUMMARY=1 TAU_IBM_BG_HWP_COUNTERS=1 TAU_TRACK_MESSAGE=1
Then anyone using TAU from that directory will get TAU_IBM_BG_HWP_COUNTERS=1, TAU_TRACK_MESSAGE=1, etc.