When using flash there are concerns with compatibility as not all computers have flash installed. Also, flash animations, often, take a while to load and this can be an issue if a visitor grows impatient. Finally, flash uses more bandwidth than standard HTML.

Flash is a vector based and hence a lightweight option for animation with smaller file size , you can express something to a visitor in a more efficient and attractive way with Flash .

Adobe Flash is known as Shockwave Flash or Macromedia , It is a software platform that is used to create the animation , the vector graphics , browser games , desktop applications and mobile apps .

Using of Adobe Flash in advertising is very popular , It displays the text and the graphics to provide the animations , It allows streaming of both audio and video clips , The creative companies are turning to Flash technology for flashier websites .

Adobe Flash  helps to give your site a more interactive and expressive outlook , With interactive features that Flash offers , like the games , the movies and feedback forms , your website will become attractive to the visitors . 

Disadvantages
Most Flash Websites lack alternative text , You can not scale the text font size , Bookmarking internal pages is not common in Flash , unless you add the proper code.

Most mobiles can´t read Flash , Most mobile devices don´t display Flash Websites ,They do not support flash websites , Flash on a website can create a barrier between you and Smartphone users , Search engine robots can´t index images .

In iPod Touch , you will get no Flash , Websites that use Flash technology tend to be slower than those that do not , you need to install Flash Player to watch flash movies , The heavier your Flash content is , the slower the Web page will load ,  It is always better to avoid excessive use of Flash in a Website.
Flash websites are slower than the sites that do not use it and this can turn visitors off , in order to watch flash movies , Flash Player needs to be installed . 

When using flash there are concerns with compatibility as not all computers have flash installed. Also, flash animations, often, take a while to load and this can be an issue if a visitor grows impatient. Finally, flash uses more bandwidth than standard HTML

1. Cross-browser compatibility

Flash is browser independent. It has no issues with cross browser compatibility. You don´t have to worry about your HTML and CSS code being interpreted differently in different browsers. As long as the Flash player plugin is installed on the user´s computer, s/he will be able to view Flash content with no issues.

2. Image Replacement for Special Fonts

Flash can be used to replace text elements on HTML Web pages with Flash equivalents. This image replacement technique is called Scalable Inman Flash Replacement

3. Interactivity

Flash supports audio, animation, and advanced video handling and interactivity. Flash is vector-based, but allows incorporation of bitmaps where needed. Flash applications can collect data, online games, feedback forms, photo slide show, audio, movies, charts, shopping carts, and different web applications that server-side scripts can do. Flash technology makes it possible to make your Website more interactive and expressive.

4. Better Expression Through Animation

Flash is vector based and hence a lightweight option for animation with smaller file size as opposed to real movie files that are raster based with much larger file size. With Flash, you can express something to a visitor in a more efficient and attractive way.

Disadvantages

1. Flash Requires a Plugin

Flash Websites require installing the Flash player plugin. If the player is not installed or if it is not the correct version then the user will be required to download or upgrade the Flash player. Do not expect that everyone will do so just to view your Website. Also many users, including myself, disable Flash by default to avoid animated advertising and to improve page-loading speed.

2. Accessibility and Usability are Impaired

Accessibility is a concern with Flash. Unless properly coded, most Flash Websites lack alternative text and can be difficult for screen readers. Users cannot scale the text font size. The back and forward browser buttons don´t work, unless you add extra code. Bookmarking internal pages is not common in Flash, unless you add the proper code, only the main page is bookmarked. Tab keystroke, an important element in accessibility, is supposed to cycle through links and Enter should activate links.

Flash is included in the Web browser as a stand alone during runtime. This means that all keyboard shortcuts, and contextual menu are lost until you click outside of the Flash area.

3. Most Mobiles Can´t Read Flash

Most mobile devices, especially Apple based devices, such as iPhone and also BlackBerry phones don´t display Flash Websites. With a growing number of people using their mobile devices for Internet browsing, creating your Website in Flash will effectively keep your mobile users out. For example in iPod Touch you will get No Flash. The Internet is slowly becoming more mobile prominent. This is a market that can´t be ignored. 

The use of flash software on a website, often, creates a very smooth, rich and interactive look and feel to a website. For a high-end customer of a company like Harry Winston or Tiffany & Co, this would be valuable as it would make them feel like the experience matches what they would expect from such a company.

When using flash there are concerns with compatibility as not all computers have flash installed. Also, flash animations, often, take a while to load and this can be an issue if a visitor grows impatient. Finally, flash uses more bandwidth than standard HTML.