Brief explanation for WM_LBUTTONDOWN windows message and DragDetect

I have a very simple question regarding this snippet(part of windows message handling in a larger switch structure that is irrelevant.):

case WM_LBUTTONDOWN:
        POINT pt = { GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam) };
        if (DragDetect(m_hwnd, pt))
        {
            OutputDebugStringW(L"drag detected!!!");
        }
        return 0;

Does "DragDetect" pause execution of the program for the time it takes to sample mouse input to determine if the mouse was dragged? If its the case, wouldn`t it be bad for performance?