I don't really use this feature often, but I quite like the concept of partial classes. It's one of those things that might not be very interesting technically, but it can be very handy.

Typically you will use partial classes to separate parts of a class that are automatically generated from those that are manually added/edited so that you can keep auto-generating without worrying about losing your manual work. I am currently working on a "proof of concept"  project and I wanted to demonstrate how a specific class would look like when the final solution would be implemented. We are interested in the complexity of this class (we want it as small and as simple as possible), so I used a partial class to "hide" the parts of the class that would not be there in the final solution (some will be auto-generated and some will become part of the framework it sits in). It's much better to be able to show somebody that it will be simple and short rather than say "trust me, when we do this properly it will be better".

Anyway, as I was happily splitting my class up into two different files I realised that I am not sure what to name the second file. I mean, the rule is that the file name needs to be the same name as the class. That's the rule. You can't break the rule. You break the rule, the whole world falls apart. But I had to break the rule, I couldn't have the same name for more than one file. Needless to say, I was panicking. Then I thought maybe I don't have to break the rule, maybe I can just come up with a new rule that takes into consideration partial classes and the world wouldn't have to fall apart.