These are my thoughts if we are only talking about IS Global Variables VS Custom Config Files
1> Its a good feature to use to store your project configuration in one place (dedicated User Interface) and IS does provide an option to retrieve the same during runtime, use global variables pipeline substitution.
2> Since it’s an OOTB feature you do not have to create custom config files and supporting flow services to write and read the key value pairs
3> They (both) not cluster aware and you have to maintain the same set of key-value pairs on all the nodes
4> If you intend to use config files, you have to create a custom config file and maintain them in the package and write underlying services to create, write, read key-value pairs or you just create the file and manually add key-value pairs and then retrieve them programmatically.
5> You have to build your own UI for custom config files to store and manage the config values
I would suggest either use service caching capability or Terracotta cache to store the config values.
Let me know if you have any further questions.
#webMethods#webMethods-General#Integration-Server-and-ESB