We have all noticed that many web sites are using flash animations to make their site more better. Flash can be used in so many ways but is it necessary to build the whole site in flash? There is some moments where you have to avoid using flash and some where it's more that OK. The disadvantages with flash are that the file size easy can become big and that will make the loading time for the page longer. Another disadvantage is that you must have Flash Player installed to view the flash content. The most people today have Flash Player installed already so this is not a very big problem.
The advantages to use flash is that you easy to make nice effects that is hard to make in the traditional way using HTML, CSS and Javascript.
It is not recommended to to build the whole site in flash. It will only result in longer loading time especially for the visitors with slower connection. It is often hard to add new things and a big site will be very clumsy. Flash menus can be alright but it's often easier to make it in the traditional way.
Flash should instead be used only when it's necessary and add extra functionality. Flash games is a excellent use for flash. A game is hard to make only Javascript and there is mostly young people that play online games so the chances are big that they have Flash Player installed. Flash movies and other tools made of flash is often a good use for flash.