*profile-symbol-list* is the list of symbols that are profiled if profile is called. Symbols in this list are monitored by the profiler to see if their function objects are on the stack when the profiler interrupts the Lisp process. The length of this list does not affect the speed of the profiling run.
*profile-symbol-list* should normally be set by one of the above functions which check that the symbol is suitable for profiling before adding them to the list.