The importance of plain text save files
Plain text save files are awesome, for many reasons, they are easier to script, if you want to regularly get some information out of your files you can do it without having to open up a big gui program or so on.
Trouble shooting is way easier, when you have the text in front of you it's most usually way easier to catch on to what you're doing wrong, many times the GUI of a program hides away a problem, and getting a different view on things can be really helpful in actually figuring out what is going on.
Also doing a quick change, here and there, or to script some bigger change over a group of files is a lot less of a hassle if you only have to deal with text, otherwise you have the option of going through all the manual hassle, or to script a GUI, which is not my definition of something that is fun to do.
As an interoperability it's also a very big plus, to make something that can parse a text file instead of some other way just makes the world so much easier, almost every programming/scripting language out there have some good way to deal with text, and it's something that you have most likely done many times before, so dealing with that instead of having to learn a new library to interface with something is usually just way easier.
Plain text is also a lot more resistance to corruption, and to fix a corrupted text file is almost always going to be way easier than some binary format, also if you're worried about harddrive space textfiles compress really well, so it's usually not much of a problem.
There is just so many plusses to plain text stuff, plain text will always be the better way to go, if you don't have a really good reason to go with something more complex, or a database, which would be the next best choice for me at least, since I can query a database with a tool and get out the information that I want that way.
So my favourite two save formats are for sure, plain text and SQL.