Building an effective website required a good deal of planing and preparation.
Previously, web developers relied on Flash to deliver highly dynamic content over the web. With the rapid evolution of browser technology, feature-rich sites can now be built using a combination of HTML, Javascript and CSS. By using these browser-native scripting languages, developers can create captivating sites while avoiding the following common problems with Flash:

• SEO: The problem with Flash is that it can’t be fully indexed by the search engines. So, stay away from it if your website strategy has any SEO expectations.

• Browsing on mobile devices: Majority of mobile devices don’t support Flash—including the highly sought after iPhone and a new web browsing device, iPad.

• Text selection: Flash is good for enhancing a story but not telling it. If your site offers information that people would want to select, copy and paste text, then using Flash is inadvisable.

• Web browser functionally: With a full Flash sites, users won’t be able to use back and forward button and browser search function (Command + F)

• Flash is currently not a W3 standard and elements simply do not exist for the data centers to evaluate what a site is about. -Flash SEO

Some people argue that they build flash sites simply to maximize the web experience.
However there are options. Here are some example of non-flash sites that deliver a comparable experience to Flash-based sites:

TavernBowl.com: Dynamic background and interactive location map.
Panic.com: Highly interactive feature map.
YouTube and Vimeo both offer HTML5 player—Flash isn’t required to view videos.

Web developers should carefully consider the needs of their clients and target audience before building a website. Since Flash is supported on a limited number of mobile devices, and isn’t SEO-friendly, it may limit the number of visitors to the site.