A Label control allows you to add text to your web page. Unlike a Literal control, a Label control supports various properties such as CssClass, ForeColor and Font that allow you to style the text that will be rendered. The Label control can also add html tags within the text property of the control.
To provide the ability to style the rendered text, the Label control renders the text assigned to its Text property wrapped in a span tag. The span tag is where the style attributes are applied. Although the addition of the span tag to the rendered markup adds only a small amount of additional bytes for each Label control, these extra bytes can start to add up if you are using Label controls inside of other repeating controls such as a GridView.
If you are not intending to use the styling capabilities of the Label control and simply need a control that can render basic text then you may wish to consider using a Literal control as it will result in slightly less markup being rendered in your page.