Banner ads have several advantages. First, they are relatively easy to produce and place. They can also be placed on specific sites, which means that you have a good level of control targeting specific audiences.

Banners also are good for "branding" -- Even if users don't click on your banner, a large audience will still see it, creating name and brand recognition. This repetition of your message may increase sales in the long run.

There are also several problems with banner ads. With the large number of banner ads on the Internet, they are becoming more and more ignored by experienced Internet users. This accounts for the diminishing "click-through" rates banners have been experiencing.

Banners also have a short shelf life -- studies have shown that most banners lose their effectiveness after about 30 days. This means that this is a marketing method that you will have to change more often than some others, to make sure that it stays fresh for the audience.

A final issue with banners is that they are intended to carry a VERY brief message -- a banner will hold the attention of a customer for about 3-5 seconds. If your message is too complicated or involved to convince a user to click in that short of a time period, a banner is probably not going to be an effective tool for you.