Linguagem C/C++ As vantagens de usar variáveis do tipo static

#include <windows.h>

LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM);
int f_static();

#define BTN_AP 1

static HWND r;

static char valor[200];
char ts[500] = "Examinai tudo. Retende o bem. \n1 Tessalonicenses 4:21";

int WINAPI WinMain(HINSTANCE hCopia, HINSTANCE hPrevInstance, PSTR szCmdLine, int iCmdShow) {
    static TCHAR szAppName[] = TEXT("Fundo Cinzento");
    HWND         hwnd;
    MSG          msg;
    WNDCLASS     wndclass;
    wndclass.style         = CS_HREDRAW | CS_VREDRAW;
    wndclass.lpfnWndProc   = WndProc;
    wndclass.cbClsExtra    = 0;
    wndclass.cbWndExtra    = 0;
    wndclass.hInstance     = hCopia;
    wndclass.hIcon         = LoadIcon(NULL, IDI_APPLICATION);
    wndclass.hCursor       = LoadCursor(NULL, IDC_ARROW);
    wndclass.hbrBackground = (HBRUSH) WHITE_BRUSH;
    wndclass.lpszMenuName  = NULL;
    wndclass.lpszClassName = szAppName;
    if(!RegisterClass(&wndclass)) {
        MessageBox(NULL, TEXT("This program requires Windows NT!"),
                   szAppName, MB_ICONERROR);
        return 0;
    }
    hwnd = CreateWindow(
        szAppName, TEXT("A Vantagem de usar uma variável static"), WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT, 400, 200,
        NULL, NULL, hCopia, NULL
    );
    ShowWindow(hwnd, iCmdShow);
    UpdateWindow(hwnd);
    while(GetMessage(&msg, NULL, 0, 0)) {
        TranslateMessage(&msg);
        DispatchMessage (&msg);
    }
    return msg.wParam;
}

LRESULT CALLBACK WndProc(HWND hwnd,UINT message,WPARAM wParam,LPARAM lParam) {
    static HPALETTE hPalette;
    static int      cxClient, cyClient;
    HBRUSH          hBrush;
    HDC             hdc;
    int             i;
    LOGPALETTE    * plp;
    PAINTSTRUCT     ps;
    RECT            rect;
    switch(message) {
        case WM_CREATE:
            plp=malloc(sizeof(LOGPALETTE)+64*sizeof(PALETTEENTRY));
            plp->palVersion    = 0x0300;
            plp->palNumEntries = 65;
            for(i = 0; i < 65; i++) {
                plp->palPalEntry[i].peRed  =(BYTE) min(200, 4*i);
                plp->palPalEntry[i].peGreen=(BYTE) min(200, 4*i);
                plp->palPalEntry[i].peBlue =(BYTE) min(100, 4*i);
                plp->palPalEntry[i].peFlags= 0;
            }
            hPalette = CreatePalette(plp);
            free(plp);

            CreateWindow(
                TEXT("static"), TEXT("A Vantagem de usar uma variável static"), WS_VISIBLE | WS_CHILD,
                10, 20, 320, 20,
                hwnd, NULL, NULL, NULL
            );
            r = CreateWindow(
                TEXT("static"), TEXT(""), WS_VISIBLE | WS_CHILD,
                10, 60, 80, 20,
                hwnd, NULL, NULL, NULL
            );
            CreateWindow(
                TEXT("button"), TEXT("Contagem usando (static int)"), WS_VISIBLE | WS_CHILD,
                120, 60, 210, 20,
                hwnd, (HMENU) BTN_AP, NULL, NULL
            );
            CreateWindow(
                TEXT("static"), ts, WS_VISIBLE | WS_CHILD,
                10, 100, 320, 40,
                hwnd, (HMENU) BTN_AP, NULL, NULL
            );
            return 0;
        case WM_SIZE:
            cxClient = LOWORD(lParam);
            cyClient = HIWORD(lParam);
            return 0;
        case WM_PAINT:
            hdc = BeginPaint(hwnd, &ps);
            SelectPalette(hdc, hPalette, FALSE);
            RealizePalette(hdc);
            for(i = 0; i < 65; i++) {
                rect.left   = i * cxClient / 64;
                rect.top    = 0;
                rect.right  = (i + 1) * cxClient / 64;
                rect.bottom = cyClient;
                hBrush = CreateSolidBrush(PALETTEINDEX(i));
                FillRect(hdc, &rect, hBrush);
                DeleteObject(hBrush);
            }
            EndPaint(hwnd, &ps);
            return 0;
        case WM_QUERYNEWPALETTE:
            if(!hPalette)
                return FALSE;
            hdc = GetDC(hwnd);
            SelectPalette(hdc, hPalette, FALSE);
            RealizePalette(hdc);
            InvalidateRect(hwnd, NULL, FALSE);
            ReleaseDC (hwnd, hdc);
            return TRUE;
        case WM_PALETTECHANGED:
            if(!hPalette || (HWND) wParam == hwnd)
                break;
            hdc = GetDC (hwnd);
            SelectPalette(hdc, hPalette, FALSE);
            RealizePalette(hdc);
            UpdateColors(hdc);
            ReleaseDC(hwnd, hdc);
            return 0;

        case WM_COMMAND:
            itoa(f_static(), valor, 10);
            if(LOWORD(wParam)==BTN_AP) {
                SetWindowText(r, valor);
            }
            return 0;

        case WM_DESTROY:
            PostQuitMessage(0);
            return 0;
    }
    return DefWindowProc(hwnd, message, wParam, lParam);
}

int f_static() {
    static int i = 0;
    return (i++);
}