Each configured user connection requires a certain amount of memory, whether or not the connection is used. The approximate overhead per user connection is 37K per user connection.
Whenever you configure additional user connections and restart SQL Server, the additional overhead reduces the data and procedure cache sizes for the server unless you also increase the memory option. Do not configure more user connections than necessary. If you increase user connections substantially, you might need to increase the memory option to give SQL Server additional memory for configuring the connections. For additional information, see "How SQL Server Uses Memory," earlier in this chapter.
The maximum number of SQL Server user connections is 32,767. Note, however, that this limit is theoretical. Because each configured user connection requires a certain amount of memory, the real limit is determined by the amount of physical memory on the computer, and the practical limit is determined by acceptable performance for your application and environment.
If the configured number of user connections are in use and a request is made for another, SQL Server returns an error.
You cannot use sp_configure to specify a configuration option higher than the current maximum value for that option.