UITableView dequeueReusableCellWithIdentifier Theory

dequeueReusableCellWithIdentifier: only returns a cell if it has been marked as ready for reuse. This is why in almost every cellForRowAtIndexPath: method you will see something like

UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

if (nil == cell) {
    cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault
                                   reuseIdentifier:CellIdentifier];
}

// Do something to cell

return cell;

In effect, enough rows will be allocated to fill the visible part of the tableview (plus one or two more). As cells scroll off screen, they are removed from the table and marked as ready for reuse. As the queue of “available cells” grows, your line that asks for a dequeued cell will start obtaining a cell to use, at which point you will not have to allocate anymore.