What's the proper use of index function?

Question

Hello! I'm having a doubt about the use of the function index(), as a best practice in Appian development. In the Appian documentation appears as: index ( data, index, default ), but I know that we can use the function as: index ( data, index, index, index... (as many as needed), default ), to navigate between an object and it returns the value needed. 
 The question is: Should I use nested index() functions? or Is better to use just one index function with many indexes inside? 
 Example: 
 {CountriesES, CountriesUS, CountriesNL} -> Cities -> Town 
 1 - Index(CountriesES, "Cities", "Town", null) 
 2 - Index(lIndex(CountriesES, "Cities", null), "Town", null).

anmolvijayvergiya · Accepted Answer

As far as I have explored the index function , Index(CountriesES, "Cities", "Town", null) could only be relevant to expression rule as it shows the below msg when we try to switch the expression mode to design mode in the interface.

Jesús Hormigos · Answer

I highly recommend only using 3 parameters in index function (normal behaviour). Using +3 params will work, but it is not the correct way to use so maybe in a future, Appian won&acute;t support it. Instead of using nested index functions manually, I suggest you create a function like this: 
 reduce(
 index(_, _, a!defaultValue(ri!default, null)),
 ri!dictionary,
 ri!path
 )

What's the proper use of index function?

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