This key defines how many threads may run at a time in the engine. This means that this many connections can be handled by the Eszter SB Egnine. There is no significant performance penalty to increase this number. The threads are started whenever a connection should be served and are stopped when the serving is finished. The only performance penalty is a small amount of memory used to administer the thread local data array. You should set this value according to the traffic of the site. The value of 10,000 should be large enough. Setting the limit lower will prevent the connections degrading your performance. Excess connection trials will be dropped but the ones that got through will be served.