I think as the debate on using tables or not, the use of iframes has been second to that.
Inline frames, also known as iframes as described by Wikipedia:
An inline frame places another HTML document in a frame inside a normal (rather than frameset) HTML. document.
The use of iframes for years has been much of a beginner’s fad in designing. It allows the user to make a small website and put all their content in a small area. However, as time passed, people were abusing this more than using frames. An iframe calls another page to load, so instead of 1, you will have more than one depending on how many iframes you have placed on your layout. Some web page newbies decided to place their content in a larger window, so now only did their content scroll, but their page, even in larger browsers.
Why not to use them?
1. Well, often the page is not indexed correctly by the search engines. Search engines will often overlook the iframe and then the design is broken. This is not good for the designer.
2. Some browsers may not show the iframe properly or at all.
3. Using the iframe could take more load time for your users. Remember, even though there is broadband, there are still people out there that only have access to the Internet via dial-up, and even if the modem handles 56K, it does not always connect even that close.
4. Using the iframe as a means to place content is not exactly a good excuse if you are allowing the window to be large in length. Rather than use the iframe, you can place your content in division layers. It is just as easy to code and makes your layout more flexible if one page is longer versus another page.
There are more efficient and better means to coding layouts than using iframes. What other reasons are there? If you are one that supports iframes, why?