The lower case extension is good to be used when you need to make sure that all the values in your data layer are converted to lower case prior to being mapped in their respective tags.
I'm not clear with what you are referring to by utag override, @zhaque
That answers my question. I was referring to "lowerqp" in Tealium Config Override - it's basically lowercase Query Parameters. So In my case I have to use both override and lower case extension (the extension doesn't lowercase the actual query parameter) but only the values.