The following was extracted from the xp-AntiSpy help file:
The connection limit was introduced by Microsoft with Service Pack 2 for Windows XP and Service Pack 1a for Windows 2003. It limits the connection requests at a time to 10. This should prevent malware from goin’ bezerk on your system and spreading its seed rapidly all around the network.
Some programs, for example filesharing software, sometimes reach the limit and therefore cannot perform as required without the limit.
Performance is not meant as bandwidth in this context.
You can check for yourself if your system reaches the limit. Take a look in the event viewer (hit start->run and enter Eventvwr.msc). When you click the System entry, take a look at the row named Event ID. If you see the number 4226 being displayed, then your system has reached the limit at that time.
To increase connection limit go to Special>Connection Limit which will bring up a dialog box with a message. Click ‘Yes,I got it’.