Difference between limit number of connections setting in IIS and the Max Pool Size

No, they are not the same thing.

• The Max Pool Size parameter affects the database server connection pooling between the webserver and the database; in case of TrackingConnectionString, the Tracking Database.

• The Limit number of connections on the IIS website configuration limits the number of connections allowed to a website, i.e. connections between clients and the web server.

  The value must be an integer between 0 and 4294967295 (unlimited). Setting the number to be unlimited circumvents constant administration if your connections tend to fluctuate. However, system performance can be negatively affected if the number of connections exceeds your system resources. Restricting a website to a specified number of connections can keep performance stable.