All state is a problem; it's something you need to keep in mind when analyzing code, because it may be used in a given computation. You need to keep it all in your head in order to comprehend what is happening.
Local state here is better than global state, especially if you consider the advice to write shorter functions - if your functions are small, so are the scopes in them, and the local state is easy to trace and memorize. Global state is not bounded, there could be hundreds of constants, enums and global objects to keep in mind.
Immutable data structures are easier to comprehend than mutable ones, because there's less points where state is modified. If you take Redux as an example, you still need to know what is in the "immutable store" at any point in order to understand how the code uses it; Redux tries to minimize the pain by limiting changes to the store in actions/reducers and by giving you access only to part of the store(local state vs global). However, you still need to understand what changes a sequence of actions perform on the store, so that's still state you need to be concerned with.
Local state here is better than global state, especially if you consider the advice to write shorter functions - if your functions are small, so are the scopes in them, and the local state is easy to trace and memorize. Global state is not bounded, there could be hundreds of constants, enums and global objects to keep in mind.
Immutable data structures are easier to comprehend than mutable ones, because there's less points where state is modified. If you take Redux as an example, you still need to know what is in the "immutable store" at any point in order to understand how the code uses it; Redux tries to minimize the pain by limiting changes to the store in actions/reducers and by giving you access only to part of the store(local state vs global). However, you still need to understand what changes a sequence of actions perform on the store, so that's still state you need to be concerned with.