difference between "set JAVA_HOME" and "setlocal" in catalina.bat for tomcat

i am new to Java and currently i wanted to set the JAVA_HOME variable in my tomcat (tocat/bin/catalina.bat) to point to my JDK installed in my system so that the servlet engine will be able to work with JAVA.

Actually i need to add the following in the batch file for that: set JAVA_HOME=C:\Program Files\Java\jdk1.8.0_45

but my question is there are already a setlocal exist in that batch file without being configured as below: setlocal

when i start the tomcat without set the JAVA_HOME variable in the batch file it just started and the page can be loaded succesfully in my web browser.

Can i know the function of this line in the batch file ? Do i need to replace this "setlocal" line with the "set JAVA_HOME=C:\Program Files\Java\jdk1.8.0_45" or just leave as it is and add one new line. Will it be affect my development later on?