I am not sure when is checking sides appropriate or not.

When I face problems like methods being called twice or some data from entity being not available, putting !world.isRemote usually solves them.

So I have quite a lot of !world.isRemote checks and I felt like I was doing something wrong.

Quote

Use this check whenever you need to determine if game logic and other mechanics should be run. For example, if you want to damage the player every time they click your block, or have your machine process dirt into diamonds, you should only do so after ensuring world.isRemote is false. Applying game logic to the logical client can cause desynchronization (ghost entities, desynchronized stats, etc.) in the lightest case, and crashes in the worst case.

This is what the documentation says and I am confused about game logic.

What exactly is game logic and how do I determine if my operation is game logic and thus should run in logical server?

And what kinds of operations should run in logical client?

56 minutes ago, lisilew said:

What exactly is game logic

Everything. (Almost)

 

Block dropping its loot? Game logic.

Swords damaging zombies? Game logic.

Crafting recipes? Game logic.

Advancements? Game logic.

Entity AI? Game logic.

Placing blocks? Game logic.

Enchanting items? Game logic.

World generation? Game logic.

 

The "things that aren't game logic" are:

User input

Graphical display

Sounds

Network communication/synchronization