What is the difference in scripts in unity between the Animation and Animator?

Question

In all the scripts i used so far when changing in the script the walk speed or adding animation clip it didn't effect it at all.

To change the character speed i need to change it in the Third Person Character (Script) > Move Speed Multiplier.

And to change animation or to add animation i need to go to the Animator window and add a new state and in the state to use the HumandoidWalk then set the state as default or in the script to use this with Play like Play("Walk")

Then what all the properties in the scripts why the speed and animation and others never effect it ? (Not talking about Nav Mesh Agent or Character Transform if needed).

For example i have a script that can accept Walk anim and then i select the HumandoidWalk but that will make the character not walking at all. Only if i make the state in the animator window then it will walk.

It's not only one specific script but in others too. I see in many places users use Animation or _animation with Play("Walk") and i to make the player move and use animation i need to use Animator or _animator.

Then what is the difference in scripts in unity between the Animation and Animator windows ? What should i use to make the character in this case ThirdPersonController to walk with animation and not just move ?

For exmaple when using waypoints i want when running the game the enemies to start walking/patrolling atuaomtic so i make new state in animator waindow with HumanoidWalk and then in the script specific for a enemy i use the Play("Walk").

Answer 1

Complexity and backwards compatibility.

Basically, when Unity was just created as a product, it was a pretty basic game engine, and a lot of systems that were necessary for game development were not very advanced. Then, a need for something with more capabilities arisen, and in a lot of cases, Unity decided to create a completely new system from scratch, and leave the old one as well.

Now we have legacy and new systems for GUI, for animation, for input handling, for particles and probably for something else I'm forgetting right now. However, it doesn't mean that old systems are completely useless: quite often, you want to use a simple and straightforward system without all the bells and whistles.

New animation system allows you to create great characters, but it also takes a lot of time to learn and set up. If you have a simple animated mesh that just needs to do the same animation on loop, I would use the old system; if I had a complicated character with several layers of different behaviours and animations created to blend with one another, I would use the new animator.

By the way, the same holds for UI: while the old system is pretty bad for working on player-looking UI, it's still widely used for quick prototypes and all kinds of debug menus.