Advantages -
1. Can control styles for multiple documents at once.
2. Classes can be created for use on multiple HTML element types in many documents.
3. Selector and grouping methods can be used to apply styles under complex contexts.
Disadvantages -
1. An extra download is required to import style information for each document.
2. The rendering of the document may be delayed until the external style sheet is loaded.
3. Becomes slightly unwieldy for small quantities of style definitions.