Alvaro Ortega : Now that we all are running fancy desktops full of powerful applications

For example....

With Libvirt I can use GUI front ends, but I can also use 'virsh' to control it.

I use the GUI for common everything stuff, but for advanced features or unusual configurations I need to edit configurations by hand:

virsh dumpxml vm-name > vm-name.xml
vi vm-name.xml
virsh define vm-name.xml

I don't need to be on the local machine either. I can use ssh or SSL/TLS to provide remote access to that particular service. I don't need to be root, nor does it really depend on me being able to know the IP address or DNS name or whatever. It can be configured ahead of time by some other person and it can just be my job to manage the VMs.

The libvirtd does sanity checking on the xml files that get uploaded and, ideally, prevents typos and mis configurations from taking down important virtual machines or screwing up other machines.

This sort of thing is good. It works on a local standalone node, or it can scale across hundreds of machines effectively. Makes scripting easier. It can be used to delegate responsibilities to individuals, control access, help keep audit trails, and all sorts of other fun stuff. Delegation and specialization is important part of managing systems in a large organization.

The GUI is just part of it.

Flat text files are indeed very simple and relatively easy to deal with as long as they are documented well. The problem is that they don't work very well in complex environments and dynamic setups. At least not by themselves. You need other mechanisms to be able to solve problems like race conditions (as a example). The other problem is lack of uniformity. It's really difficult to write a script or a program that can deal with all the differences methods and formats that different Linux services use.

Makes automation very difficult and automation is the key to scalability and correctness. Without it your stuck with a very labor intensive and error prone processes. Going "cd /etc/ ; sudo vi foo/blah.cfg; service restart foo" is simple, but it is not terribly useful when dealing with 400-500 nodes... nor is it pleasant when its a configuration change that commonly happens on your desktop or laptop (such as giving a WPA password to a new network when your travelling).