Quote Originally Posted by Raffles View Post
As an example, people might want to split it up to put advertising in the middle of it.
Would they really want to split the list to insert advertisment, or would they just want the advertisement to appear in the middle of the list?

In the first case, they're breaking semantics by splitting a single list into two.
In the second case, just use CSS to make a hole and position the ad in that space.

Quote Originally Posted by Stormrider View Post
Or, step by step instructions that are split into larger sections, eg days. You have a day 1 section with steps 1-12 maybe, then a day 2 section, new header and introduction paragraph, with steps 13-27 etc...
Separate lists, or nested lists.
The Day 2 list is not a continuation of the Day 1 list; it's a separate list that describes the set of steps to be taken on day 2.
Alternatively, the day header and introductory paragrahs should be part of the list items.

Quote Originally Posted by Stormrider View Post
There are lots of reasons why you might want to.
I'd say there are lots of reasons why you might think you want to, but if you stop to think about what you're doing you'll see that it's not really necessary.

HTML is about semantics and structure, not presentation. Perverting the markup for presentational purposes is so last century. We should use CSS to control presentation now.