There are use cases when row selection and row checking are two seperate, independent operations.

One example is a mail client.

The selected row might be opened in a preview pane.

You might still be able to check multiple rows to delete, or move, or otherwise operate upon without changing the selection.

Ext.ux.GridRowChecker is a Grid plugin which offers this.

Drop the code below into examples/grid as array-grid.js. It adds Record[] checkChecked(), void checkAll() and void uncheckAll() to its client GridPanel.

Code:
Ext.onReady(function(){

    Ext.state.Manager.setProvider(new Ext.state.CookieProvider());

    var myData = [
        ['3m Co',71.72,0.02,0.03,'9/1 12:00am'],
        ['Alcoa Inc',29.01,0.42,1.47,'9/1 12:00am'],
        ['Altria Group Inc',83.81,0.28,0.34,'9/1 12:00am'],
        ['American Express Company',52.55,0.01,0.02,'9/1 12:00am'],
        ['American International Group, Inc.',64.13,0.31,0.49,'9/1 12:00am'],
        ['AT&T Inc.',31.61,-0.48,-1.54,'9/1 12:00am'],
        ['Boeing Co.',75.43,0.53,0.71,'9/1 12:00am'],
        ['Caterpillar Inc.',67.27,0.92,1.39,'9/1 12:00am'],
        ['Citigroup, Inc.',49.37,0.02,0.04,'9/1 12:00am'],
        ['E.I. du Pont de Nemours and Company',40.48,0.51,1.28,'9/1 12:00am'],
        ['Exxon Mobil Corp',68.1,-0.43,-0.64,'9/1 12:00am'],
        ['General Electric Company',34.14,-0.08,-0.23,'9/1 12:00am'],
        ['General Motors Corporation',30.27,1.09,3.74,'9/1 12:00am'],
        ['Hewlett-Packard Co.',36.53,-0.03,-0.08,'9/1 12:00am'],
        ['Honeywell Intl Inc',38.77,0.05,0.13,'9/1 12:00am'],
        ['Intel Corporation',19.88,0.31,1.58,'9/1 12:00am'],
        ['International Business Machines',81.41,0.44,0.54,'9/1 12:00am'],
        ['Johnson & Johnson',64.72,0.06,0.09,'9/1 12:00am'],
        ['JP Morgan & Chase & Co',45.73,0.07,0.15,'9/1 12:00am'],
        ['McDonald\'s Corporation',36.76,0.86,2.40,'9/1 12:00am'],
        ['Merck & Co., Inc.',40.96,0.41,1.01,'9/1 12:00am'],
        ['Microsoft Corporation',25.84,0.14,0.54,'9/1 12:00am'],
        ['Pfizer Inc',27.96,0.4,1.45,'9/1 12:00am'],
        ['The Coca-Cola Company',45.07,0.26,0.58,'9/1 12:00am'],
        ['The Home Depot, Inc.',34.64,0.35,1.02,'9/1 12:00am'],
        ['The Procter & Gamble Company',61.91,0.01,0.02,'9/1 12:00am'],
        ['United Technologies Corporation',63.26,0.55,0.88,'9/1 12:00am'],
        ['Verizon Communications',35.57,0.39,1.11,'9/1 12:00am'],
        ['Wal-Mart Stores, Inc.',45.45,0.73,1.63,'9/1 12:00am']
    ];

    // example of custom renderer function
    function change(val){
        if(val > 0){
            return '<span style="color:green;">' + val + '</span>';
        }else if(val < 0){
            return '<span style="color:red;">' + val + '</span>';
        }
        return val;
    }

    // example of custom renderer function
    function pctChange(val){
        if(val > 0){
            return '<span style="color:green;">' + val + '%</span>';
        }else if(val < 0){
            return '<span style="color:red;">' + val + '%</span>';
        }
        return val;
    }

    // create the data store
    var store = new Ext.data.SimpleStore({
        fields: [
           {name: 'company'},
           {name: 'price', type: 'float'},
           {name: 'change', type: 'float'},
           {name: 'pctChange', type: 'float'},
           {name: 'lastChange', type: 'date', dateFormat: 'n/j h:ia'}
        ]
    });
    store.loadData(myData);
    
    Ext.ux.GridRowChecker = Ext.extend(Object, {
	    header: "",
	    width: 23,
	    sortable: false,
	    fixed: true,
	    menuDisabled: true,
	    dataIndex: '',
   		id: 'selection-checkbox',
	    rowspan: undefined,

    	init: function(grid) {
    		this.grid = grid;
    		this.gridSelModel = this.grid.getSelectionModel();
    		this.gridSelModel.originalMouseDown = this.gridSelModel.handleMouseDown;
			this.gridSelModel.handleMouseDown = this.onGridMouseDown;
    		grid.getColumnModel().config.unshift(this);
    		grid.getChecked = this.getChecked.createDelegate(this);
    		grid.checkAll = this.checkAll.createDelegate(this);
    		grid.uncheckAll = this.uncheckAll.createDelegate(this);
    	},

		renderer: function() {
			return '<input class="x-row-checkbox" type="checkbox">';
		},

		getChecked: function() {
			var result = [];
			var cb = this.grid.getEl().query("div.x-grid3-col-selection-checkbox > input[type=checkbox]");
			var idx = 0;
			this.grid.store.each(function(rec) {
				if (cb[idx++].checked) {
					result.push(rec);
				}
			});
			delete cb;
			return result;
		},

		checkAll: function() {
			this.grid.getEl().select("div.x-grid3-col-selection-checkbox > input[type='checkbox']").each(function(e){
				e.dom.checked = true;
			});
		},

		uncheckAll: function() {
			this.grid.getEl().select("div.x-grid3-col-selection-checkbox > input[type='checkbox']").each(function(e){
				e.dom.checked = false;
			});
		},

		onGridMouseDown: function(g, rowIndex, e) {
			if (e.getTarget('div.x-grid3-col-selection-checkbox')) {
				e.stopEvent();
				return false;
			}
    		this.originalMouseDown.apply(this, arguments);
		}
    });

    // create the Grid
    window.grid = new Ext.grid.GridPanel({
        store: store,
        plugins: [ new Ext.ux.GridRowChecker() ],
        columns: [
            {id:'company',header: "Company", width: 160, sortable: true, dataIndex: 'company'},
            {header: "Price", width: 75, sortable: true, renderer: 'usMoney', dataIndex: 'price'},
            {header: "Change", width: 75, sortable: true, renderer: change, dataIndex: 'change'},
            {header: "% Change", width: 75, sortable: true, renderer: pctChange, dataIndex: 'pctChange'},
            {header: "Last Updated", width: 85, sortable: true, renderer: Ext.util.Format.dateRenderer('m/d/Y'), dataIndex: 'lastChange'}
        ],
        stripeRows: true,
        autoExpandColumn: 'company',
        height:350,
        width:600,
        title:'Array Grid'
    });

    grid.render('grid-example');
    grid.getSelectionModel().selectFirstRow();
});