Should I use unnamed namespaces in implementation files?

I have defined some functions (no classes involved here) in an external *.cpp file, and of course there is an appropriate *.h file.

Some of the functions in the *.cpp file are used only in that *.cpp file nowhere else. They are not even mentioned in the *.h file.

Should I put those functions into an unnamed namespace or may they live just next to the other functions? And if so, why should I need an unnamed namespace for them? I cannot see a problem, since those functions are not accessible from outside anyway.