1. Web animations are used:
for advertising
Infographics
Banner advertising (space on websites)

2. Banners on the web come in different sizes
You must use specific standards sizes and also follow guidelines from the IAB (internet advertising bureau –UK)
Most advertisers use google guidelines, to make it simple:
Animations must not be longer than 30 seconds
Shorter animations can loop or repeat, but must stop after 30 seconds
All information should be accurate and descriptive of what you’re advertising
Read Google advertising policies to help you understand web advertising rules:

3. While you are there Read this article from Steve JoB
Give at least 5 reasons why it is not advisable to make Flash Animations for the web.