When to Use Multiple Video Title Sets?

[BassPig]

When authoring a DVD, one has a number of choices about how the structure of the disk scenario is built.
I have built a number of projects with just one Video Title Set and one
language, under which all the program streams exist.

The question I have is, What types of projects would benefit from using more
than one VTS?
How would these scenarios be structured? Does the VTS exist per language?
Ie., if a DVD is to be released only in English, is there any reason to use
more than one VTS?

Most of us who author DVDs are aware that the first program chain is what
gets played when the disk is first inserted in the player. That usually has
a post command that chains to a main menu or root menu. From the root,
multiple possibilities exist and from what I can tell, it appears possible
to do just about any kind of scenario within just one VTS. Am I missing
something here as to the use of more than one VTS in a project?

[ebina]

I wanted to create a DVD with some video that was 4:3 aspect ratio, and some video that was 16:9 aspect ratio.

I had to use multiple VTSs for this as you can only have one aspect ratio per VTS.

[BassPig]

That's a good point. I had not thought of that.
I was thinking more in terms of discs with various language versions of a program on them, but that may even be possible under the same VTS.

Are there any other structures, besides multiple aspect ratios, that would benefit from or even require the use of multiple VTS?

In terms of menu construction within the SAME aspect and language, would it be correct to assume that all authoring would be done in the same VTS?