Files must load and be applied in an orderly manner. Flooding of the sockets with requests is unacceptable. No big bandwidth demand should be felt by the client at any instant in time. The number of active file requests should not exceed available streams. Images need to be fully loaded before use.
Partial images spoil the existing effects and makes the page feel incomplete and waiting.
Once loaded the page needs to be able to stand-alone. Any need to reload an image from the web is unacceptable. Note, a long standing page in a browser might have it's images expire in cache. This is unavoidable. Internet Explorer cache problems.