One of the biggest advantages of Cascading Style Sheets is that it helps in maintaining the consistency of your website. To make your site consistent enough, you need to build external style sheets. External style sheets can be used in two different ways: one is to link the external style sheet and the other one is to import the style sheet. By using external style sheets, you can see all your web pages will have identical styles.

The advantages of external style sheets are numerous. You can exert control on the look and feel of various documents at a time. This will be successful if you have a group of people to build your website. It is an uphill task to memorize a large number of style rules. There is also a printed style guide to help your cause. But it is not a feasible idea to go through the guide every time a doubt creeps into your mind. It is an efficient and tedious way of doing things.

External style sheets also help in building classes of styles that can be employed on different HTML elements. If you make use of a particular font type to emphasize several elements on your web page, then you can generate a class of that font type and establish it in your style sheets to build emphasis. So you get rid of defining a particular style for all the instances of the emphasis one by one.

Using external style sheets, you can have your styles at one place easily and this leads to more efficiency. You can use all the grouping techniques available in CSS on your external style sheets. The flexibility and control is what you will have on your web pages.

On the other hand, these style sheets have certain loopholes. If your external style sheets are very large, then they can raise your download time. Similarly, if your style sheets consume less bytes, your website will be very complicated. The same problem occurs in case of delivering of tables. You have to wait for the whole style sheet to be loaded before the page is viewed. The volume of external style sheets keeps increasing rapidly as it is hard to say when a specific style ceases to exist. Even though the web page containing that style is removed, the style still persists in the style sheet.

External style sheets are generated in the same way as other document level style sheets. The syntax is the same. But you need to include a selector and the declaration. The syntax is as follows:

selector {property : value;}