Why 'target datalayout' strings are in .ll modules?

What is the meaning of 'target datalayout' being in .ll in addition to 'target triple'?
When it can be meaningfully changed having the same 'target triple'?

As I understand llvm derives most of architecture-specific information from 'target triple'. For example ABI used by llvm is keyed to 'target triple'. But some parts of ABI are in 'target datalayout'. For example, on MacOS the fact from ABI that all stacks are always 16-aligned during procedure call is defined in 'target datalayout', not by 'target datalayout' like most other parts of ABI.

So why 'target datalayout' is exposed in .ll?