The reason for changing the port is to eliminate the need to specify the port in the URL. If you leave the setting as-is, then the URL for BO is http://server:8080/BOE/BI. If you change the port to 80, then it can be left off: http://server/BOE/BI.
This will not work if there is another web server running on the same machine that is also on port 80. If this is the case, Tomcat will not start at all.
To change the port setting, open up tomcat\conf\server.xml, and simply replace “8080” with “80”.