The disposal method specifies what happens to the previous frame after the current one is displayed. The disposal method works with transparency, so if your frames aren't transparent you don't have to worry about it. To move frames within a larger frame, use Restore to Background to avoid multiple images. Netscape 2.02 had a memory leak that caused it to bomb or freeze when animated GIFs ran too long, but this was fixed in 3.0 so keep that in mind. Giving the browser some CPU cycles lets the rest of the page load, allowing users to negotiate links more easily.
Some sites require banner ad loops to end in less than four seconds.
You can specify the delay between any two frames to simulate any effect you want. This made us laugh, but beta testers complained that it ate up their CPU's, even on high-end machines. Starting the penguin off screen solved the problem.