Animating in Flash can be done either by using key frames and animating your assets on the timeline, or by using Actionscript and coding the required movements into the code.
Initially animating in code will take longer than using timelines and key frames, but if your project may change down the line and you need to change some elements of an animation, amending parameters in the Actionscript code will take less time than adding new key frames, adjusting tweens etc.
Setting up animation in Actionscript means setting variables such as animation speed, movement co-ordinates and time frames. If you animate a movie clip within Flash which then needs changing – for example it’s animation speed, or ending X/Y co-ordinates, then a simple change to a variable is needed, and the resulting animation changed. This type of amendment can be done in seconds and allows for quick refinements of the animation with immediate feedback.
Ultimately writing the animation in code will save you time towards the end of a project when possible deadlines and targets need meeting and lengthy adjustments of timelines are not possible. And once you have one animation done, you can re-use the same code for other assets and save even more time.