It's a bit of a legacy transformer, it would allow you to call specific functions as used internally by FME, as listed here: http://docs.safe.com/fme/html/FME_FactFunc/nav.html#function_header

The functions are the same as used in the FME transformers, but the difference is that the FMEFunctionCaller gave you a bit more flexibility in edge cases and would allow you to dynamically parametrize the call in a way that wasn't possible in earlier versions of FME. Today you can parametrize pretty much all the transformer settings and you can also access the same functions inside a lot of other transformers such as the AttributeCreator using the advanced editor.

So I'm not sure the FMEFunctionCaller is very useful today, I sure haven't used it in ages.

sounds like a 0 point winner!

As David says, most functions are now created as transformers, and many are exposed in the AttributeManager text/arithmetic editors.

The one I use the most is probably the CopyAttributes function, where I'm doing something complex with defining a new attribute using some other item as the attribute name (though even that you can mostly do with the AttributeCreator transformer). The only instance I can find where I used this transformer was in a workspace I created for FME Golf - which is hardly evidence of best practice!

Thanks !!!

Thanks Mark