On iOS, what is the difference between adding a subview to a UITableViewCell object "cell" vs to "cell.contentView"?

I believe If I am not wrong, the contentView is a subview of UITableViewCell.

If you look at this page here, you can see there are actually 3 subviews in a UITableViewCell

I think by default, the Editing Control is hidden until you enter edit mode for a table in which case, the Editing Control appears (the minus button left of each row) and your contentView gets resized and pushed to the right. This is probably what gives the "proper animation" effect mentioned by the other answer.

To test the difference, try adding a subview such as UILabel with text, to the cell rather than the cell.contentView. When you add it to cell rather than cell.contentView and you enter edit mode for your table, I believe your UILabel will not resize, you will see the edit button ontop/below the minus sign button.

Placing your views in the contentView affects proper animation in and out of edit mode. Place all of your subviews in contentView when you're not subclassing, which should be all of the time unless you know what you're doing.