官方文档

Update Order

When you’re keeping track of game logic and interactions, animations, camera positions, etc., there are a few different events you can use. The common pattern is to perform most tasks inside the Update function, but there are also other functions you can use.

FixedUpdate

FixedUpdate is often called more frequently than Update. It can be called multiple times per frame, if the frame rate is low and it may not be called between frames at all if the frame rate is high. All physics calculations and updates occur immediately after FixedUpdate. When applying movement calculations inside FixedUpdate, you do not need to multiply your values by Time.deltaTime. This is because FixedUpdate is called on a reliable timer, independent of the frame rate.

Update

Update is called once per frame. It is the main workhorse function for frame updates.

LateUpdate

LateUpdate is called once per frame, after Update has finished. Any calculations that are performed in Update will have completed when LateUpdate begins. A common use for LateUpdate would be a following third-person camera. If you make your character move and turn inside Update, you can perform all camera movement and rotation calculations in LateUpdate. This will ensure that the character has moved completely before the camera tracks its position.

自己的理解

Update()是实机帧调用,受GameObject的渲染影响,每次的Time.deltaTime都是不一样的
而FixedUpdate()则是固定间隔,风雨无阻,游戏多卡FixedUpdate()也会按时调用
LastUpdate()是紧跟Update(),给Update()擦屁股的函数

所以官方建议在FixedUpdate做一些物理引擎相关的事