Is c-indent-line-or-region already doing the same thing as smart-tabs?

[john smith]

In Emacs 24.5.1 is c-indent-line-or-region already doing the same
thing as smart-tabs or do I miss something?  As I tried this snippet
from https://www.emacswiki.org/emacs/SmartTabs:

    int f(int x,
    int y) {
    return g(x,
    y);
    }

I got exactly same result when marking the whole function and pressing
Tab key regardless of smart-tabs-mode state.  It seems that
c-indent-line-or-region can add both spaces and tabs on its own.  Is
my thinking correct?  Are smart-tabs needed for other other modes
apart from C?

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