Smarty

[AnrDaemon]

I'm struggling to get the full picture of Smarty::$compile_id implications.
I understand, that specifying a distinct compile_id for same template will produce a separate compiled version of it. But in which cases the versions would be actually different? (Or, in other words, the use of compile_id actually do make sense.)
Perhaps, someone can do a sanity check on the following list, please?
The documentation hinting on these two possible cases:

1. Compile-time transformations. Quite obvious, when you transform the same template in multiple ways, you end up with an actual different templates.
2. Shared compiled template cache for independent sets of similarly named template sources. That's… questionable practice, but I think I understand the implication.

Is there any other cases?

[U.Tews]

1. The compile_id should be used when running the template through different pre- or post-filters during compiling.

2.In Smarty 2 templates with same name from different template_dir did compile in same compiled template, so it did make sense there. This is not the case in Smarty 3.

3.Currently template inheritance is a compile time process. An {extends} tag with a variable template name did require different compile_id. This restriction will be removed with 3.1.28 where inheritance will become a runtime process.

[AnrDaemon]