Why we use "use lib $path"?

If we are trying to add a module or library files in our program using require or use statement then it will search that module or library files in the Perl's default search path.

The statement use lib is used to add the directories to default search path.

So if the module or library file is not located in the Perl's default search path then it will find the library files in the path we have given with the use lib $path.