In your case, there's not much of a problem. The reason modules (and namespaces) exist is becuse related functions belong packaged together, and you should have ability to use a function from another namespace that might end up conflicting with a function in your namespace.

If you had an add_it() function that you didn't want overwritten, you could use your module as

use MyModule;
print MyModule::add_it($amount);
[download]

And when multiple modules have the same function names (this is most common with classes -- objects, I mean), they need to be able to keep their own functions separate to themselves.